The Infected

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"I'll see peace back on Earth if I've gotta murder every one of these animals with my own bare hands!"

―Bill

"It's them or us!"

―Coach

The Infected are Left 4 Dead's take on the classic movie and pop-fiction zombie. But rather than being undead, they are living humans who have been Infected by the Green Flu virus, causing massively increased aggression and loss of many higher brain functions such as speech and self-preservation. Like cinematic zombies, those present in the Left 4 Dead series attack human victims and will attempt to bite them, unless they are immune.

Characteristics

In the case of Common and Uncommon Infected, observed aggressiveness manifests itself primarily in the form of frenzied physical blows and kicks. Bite attacks are of a secondary nature and may even be incidentally delivered. The Infected primarily attacks uninfected humans who have attracted attention through noise, movement and displaying bright lights. It is unknown whether other sensory stimuli such as smell or color variation trigger attack responses. Common Infected are also frequently observed displaying mutual aggressiveness towards one another. However, these attacks are not shown when the Infected finds an un-infected human.

The Infection might also have changed their physiology. Some infected suffer instant fatal tissue damage, and dismemberment from moderate blunt force, yet they can still jump down from heights of approximately 20 feet with perfect physical coordination and without harm. They have no fine motor control and their gross motor control functions are heavily degraded, thus rendering them incapable of picking up objects and operating simple mechanisms such as door handles.

When passive and unstimulated, Common Infected lean against a support (such as a wall), sit, lie recumbent or stagger aimlessly in short uncoordinated steps. Many will vomit profusely or display visual signs of being unwell (e.g. slumped over cradling the head). Uncommon Common Infected tend to be less inert in their passive state since they are invariably observed to be in a standing posture.

When active and stimulated, Common Infected undergo a rapid transformation during which their speed of movement is rapid, their gait is highly coordinated and focal direction unerring. Uncommon Common Infected display the same behavioral qualities with the exception that they appear to be more sensitive to external stimuli and are thus more easily aroused and provoked.

Through some unknown mechanism, a small percentage of Infected humans will undergo a dramatic mutation, eventually turning into one of the Special Infected. There are nine varieties of the Infected, seven of which are playable. Eight varieties are considered "Special Infected," which have special abilities in addition to doing more damage against the Survivors. In turn, two of these eight varieties are considered "Boss Infected", namely the Tank and the Witch.

Common Infected

Main article: Common Infected

A crowd of Common Infected in Left 4 Dead 2

Common Infected, as their name implies, are the most commonly faced enemy and are the easiest to defeat. They are more akin to the antagonists from the film 28 Days Later than to the typical shambling cinematic zombie. They are exclusively AI-controlled and fairly weak. Their strength lies in their tendency to attack in large groups of up to several dozen, known as Hordes.

However, the danger they pose must never be underestimated. Common Infected can easily bring down health on Expert as every claw attack brings down your health by 20 (10 if hit from behind), unlike Easy (1 from front, 0.5 from behind), Normal (2 and 1) and Advanced (5 and 2.5). While they seem capable of ignoring pain, they can still be killed easily. They are capable of climbing ladders and scaling objects, as well as breaking down weak walls and doors. They cannot break down the beginning safe room door (unlike the Tank), so you should be relatively safe inside a closed safe room. This type of Infected are attracted by flashlights, loud noises such as car alarms, or by Boomer bile. They appear to lack self-preservation, but do appear to have some intelligence, as in the Hard Rain or The Passing campaign; the Horde will attack when the storm picks up and there is minimal visibility (or maybe they get really aggressive or get attracted to the lightning and noise of the storm).

Throughout Left 4 Dead, the physical appearance and dress of Common Infected are consistent with the particular location being visited. For example, in Mercy Hospital, they are medical staff, patients and maintenance personnel, whilst at Metro International Airport Common Infected include flight, cabin and ramp crew plus business executives. In more neutral locations such as Riverside or Daughtery Farm, Common Infected appear as generic "everypersons," including servicemen wearing camouflage, blue collar and office workers and young adults through to late-middle-aged individuals of both genders. The same principle applies throughout Left 4 Dead 2, but given this game's diverse locales, the range of physical variation displayed is considerably wider relative to Left 4 Dead.

Horde

"Here they come!"

―Louis

A horde as one would appear in the Farmhouse Finale.

Common Infected attack in a horde.

A horde is a large group of Common Infected (sometimes Uncommon Infected included) that will rush the Survivors either at random intervals, during the finales, as a response to Boomer bile/bile bombs, or in response to loud, high-pitched noises and/or bright lights (car alarms, most alarms or noises during Panic Events, pipe bombs).

Uncommon Infected

Main article: Uncommon Infected

Left 4 Dead 2 introduced six special types (seven counting Jimmy Gibbs Junior) of Common Infected known as "Uncommon Common Infected," "Uncommon Common," or simply "Uncommon Infected." Each Uncommon Infected is unique to the campaign it appears in.

Dead Center features the CEDA Worker Infected (which are immune to fire and may have Bile bombs attached to them) and Jimmy Gibbs Junior, The Passing features the Fallen Survivor (who may carry a First aid kit, Molotov, Pipe bomb or Pain pills), Dark Carnival features the Clown Infected (which have squeaky shoes that attract surrounding Common Infected), Swamp Fever features the Mud Men (each hit slightly blinds a Survivor's vision, they also crawl swiftly around on all fours), Hard Rain features the Worker Infected (who have earmuffs, so they don't chase Pipe bombs and strangely, are immune to the attraction of the Bile bomb, but that is only if it doesn't hit an Infected), and The Parish features the Riot Infected (who can only be killed by attacking them from behind due to their body armor). Each Uncommon Infected has its own special ability that make them slightly more dangerous than Common Infected.

Special Infected

The Special Infected have been heavily mutated by the Infection, giving them "special abilities." Each generally has a unique ability that a Survivor cannot face alone, making them the true teamwork testers in this game. They are not attracted by car alarms or loud noise and have a higher degree of intelligence than Common Infected, being able to run away if required and setting up ambushes.

They are also more aggressive than the Common Infected, as they will actively attack Survivors rather than passively sitting in a stupor until disturbed (except for the Witch and the Tank, which will wait for the Survivors to alert or attack them). They are deadly to lone survivors, but can be avoided and defeated through communication and synergy. The Director is able to spawn them at any time according to the difficulty and how the Survivors are doing. If you are playing online, it is best to note that there is a special infected around

Seven of the Special Infected are playable by human players in the following gameplay modes:

• Versus
• Realism Versus
• Scavenge
• Various Mutations

Playable

The Boomer

Main article: The Boomer

The Boomer is a Special Infected that vomits a special bile at Survivors, which temporarily blinds them and draws Common Infected to them. At a distance the Boomer isn't much of a threat; his large size and low health make him an easy target against any weapon at mid or long range. However, if within range he can vomit on Survivors, attracting the Horde.

When he dies, he explodes, covering any Survivors who are close enough with bile, blinding them and causing them to stumble backwards. The Boomer is notorious on the Expert difficulty for being able to snipe Survivors. Boomers can be anticipated because of the near-constant gurgling they make. In Left 4 Dead 2, there is also a female Boomer, although the gender has no effect on gameplay.

The Hunter

Main article: The Hunter

The Hunter is a Special Infected that is not as mutated on the outside. The Hunter is extremely fast and agile, capable of quickly scaling walls. Additionally, he can pounce and pin down Survivors, clawing at their abdomen until either the victim is dead or the Hunter has been knocked off or killed by another Survivor. They are not the most physically robust Infected, having relatively low health, and thus it doesn't take very much to kill them.

When the Hunter crouches down in preparation to pounce, it growls, giving it away to any nearby Survivors. However, whilst standing, it makes no noise. The Hunter is the only Special Infected that can remain absolutely silent. In Left 4 Dead 2, they can be killed with a melee weapon while in the state of pouncing by aiming upwards and hitting, although this is fairly difficult, as timing is vital and it's easier to kill them from a distance with a high-powered primary weapon.

The Smoker

Main article: The Smoker

The Smoker is an ambush class that can strangle Survivors with its long tongue, similar to Half-Life's Barnacle. The help of another Survivor is required to escape from a Smoker's hold (though if quick enough it is possible, though difficult, to kill a Smoker who has already grabbed you, earning an achievement). As the name implies, Smokers emit smoke when killed to impair Survivors' vision.

A Smoker also will frequently cough, letting the Survivors know when he is in the area. The Smoker can drag players that he has captured with his tongue towards himself, though he remains stationary and cannot move. The Smoker is also momentarily paralyzed for a few seconds after having his tongue removed from his captive by another Survivor. In Left 4 Dead 2, the Smoker has six tongues, but this has no effect on gameplay.

The Tank

Main article: The Tank

The Tank is the biggest and strongest of all the Infected and is reasonably fast, only slowing if hit with large amounts of automatic weapons fire or when lit on fire (Versus in Left 4 Dead only and any mode aside Versus on Left 4 Dead 2). He is the only player-controllable "Boss Infected." If any Survivors at 40% or above health (including health gained from Pain pills or the Adrenaline Shot) are running away from the Tank, it will not be able to catch them, as they can run slightly faster (unless the Tank in question is an AI Tank in Left 4 Dead).

The Tank has incredible strength and resistance―his punch can send Survivors flying, rendering them temporarily defenseless, and in Expert mode, instantly incapacitate them. The blow can send Survivors off high hazards to their deaths. He is also capable of throwing chunks of concrete that he rips out of the ground to momentarily stun Survivors and dealing the same damage as a punch from a Tank. It can also punch large objects in the direction of Survivors with enough force to incapacitate them instantly.

Nevertheless, the Tank will die within 30 to 45 seconds if set on fire (varying with the difficulty), except in Versus. When controlled by a player, the Tank has a "Control Meter"; unless the player is able to locate the Survivors and hit one of them, the Control Meter of the Tank will slowly lessen, and once it runs out, the player will lose control of the Tank to another randomly assigned player. When idle, the sound that a Tank makes is heavy breathing. The Survivors are alerted of an approaching Tank by dramatic music, furious roars and, when he is dangerously close, the screen will start to shake. The Tank's Music Cue

The Charger

Main article: The Charger

The Charger is a Special Infected that appears in Left 4 Dead 2. The Charger's main attack is charging forward and plowing into the Survivors. On a successful charge, he will grab and carry a single Survivor while knocking down the others. Once the Charger has hit a wall or other surface, or after he has run a certain distance, he will begin slamming his captive into the ground until an ally frees them. If he misses and hits a wall, he will stumble, leaving him open to attack.

The Charger can be detected by the Survivors by the warped growling noise he makes. He will announce his charge with a loud bellow. The Charger appears to have a rocky or calloused surface on his larger right arm, which may be what he uses to inflict most of his force when charging, while his other arm appears to have no bones or muscle.

Because of his hulking size, the Charger cannot be shoved off with melee, and must be killed in order to release his victim. If a Survivor has explosive rounds, they will dislodge the Charger from the Survivor and stumble him. Any Survivor that has been knocked out of the way during his charge will fly a considerable distance and slowly stand back up, making the Charger a deadly foe in cramped hallways or near high passageways. He is also the strongest and most durable of the Special Infected (excluding the Tank and the Witch); additionally, his melee attacks are very strong and can easily incapacitate a weakened Survivor.

The Jockey

Main article: The Jockey

The Jockey is a Special Infected that appears in Left 4 Dead 2. He is a small Infected that attacks Survivors by clinging to them from behind and literally riding the Survivor while attacking them. He can shift his weight around and cause the Survivor to stumble in his desired direction, giving this Special Infected a type of control over the Survivor.

Survivors who are being ridden by the Jockey can attempt to "resist" the Jockey, which will allow other players a chance to catch up and knock the Jockey off. Jockeys can ride Survivors into dangerous situations, such as into natural hazards, Witches, or other Infected; a Jockey can also pull a Survivor off of a ledge, causing them to become incapacitated, or riding them to their death if they are not resisting. The Jockey seems to have a spinal disease, similar to kyphosis, giving him a hunched appearance. He also has a maniacal laugh and is constantly twitching, giving him a sort of hyperactive nature.

The Spitter

Main article: The Spitter

The Spitter is a new Special Infected in Left 4 Dead 2. She possesses the ability to spit a green ball of acid from long distances, which, upon hitting the ground, will expand into a large puddle and damage any Survivors who make contact with it. After spitting, however, the Spitter is temporarily paralyzed for a second, giving the Survivors a chance to kill her.

The longer the Survivor stands in it, the more damage the Survivor takes from the goo. This ability allows the Spitter to aid other Special Infected; for instance, if a Hunter pounces a Survivor, a Spitter can spit upon that Survivor, causing even more damage. However, in spite of such a useful ability, the Spitter is very weak in terms of health, so taking out a Spitter will be an easy task.

Upon death, the Spitter leaves a similar, smaller kind of puddle that has the same effect on the Survivors. She is one of the most powerful Infected if Survivors are caught standing in her spit, and are too distracted to move quickly due to other Infected or a lack of awareness at damage being dealt. On Scavenge Mode or any finale requiring gas cans, when they are dropped, the Spitter's goo will ignite them if left in the goo long enough.

Computer-Controlled

The Witch

Main article: Witch

The Witch generally only appears a few times per campaign, and is passive unless provoked by flashlights, gunfire, or Survivors in close proximity. She is the second "Boss Infected." Pistol fire does not provoke her easily, but it will do only a small amount of damage. She is very powerful, capable of incapacitating, and even killing Survivors with one hit. When the Director spawns a Witch, the faint chord of the Witch music will play, allowing veterans of the game to quickly prepare for the "obstacle."

The Witch cries loudly, which Survivors will mention they hear, warn you to turn off your flashlight, and dramatic music will play. While the Witch can be killed, it is best to avoid startling her unless absolutely necessary. The most common means of her being startled is by staying near her too long or bumping into her. The flashlight will quicken her agitation rate, as she stands up faster with a flashlight shone near (or on) her. If you attack her, or if someone else startles it, it will say "[Survivor's name] startled the Witch". If a Special Infected like the Jockey or Charger gets too close to the Witch and a person was targeted and hit her, it will say, "You startled the Witch! Best not to disturb her next time."

The Witch is very rarely found in small rooms and normally stays off the main route, but has been found in front of safe rooms (or even inside the safe room), doorways, and in the middle of streets. Once a Witch has killed a Survivor, she will retreat out the area and completely disappear. However, in some strange cases, the Witch has been known to kill the closest Survivor to her. This does not usually happen, and when it does, the Witch runs off as normal after killing the Survivor.

Also, if a survivor blocks the Witch from attacking the Survivor who startled her, she will attack the Survivor blocking her and either incapacitate the blocking player and run away or incapacitate both the blocking player and the player who startled her. If the Witch is lit on fire (Molotov, Incendiary ammo, Gas can) while she is chasing a Survivor, she will immediately start chasing after whoever burned her. Even if she is retreating, if she is lit on fire, she will go after that Survivor even though she either killed another Survivor or one locked themselves in a safe room.

• The Witch's music cue.

The Wandering Witch

Main article: The Wandering Witch

The Wandering Witch appears in Left 4 Dead 2. She is seen only in the daylight hours, aimlessly wandering around and sobbing loudly with her head in her hands. Her constant movement makes The Wandering Witch harder to avoid, but she is also far more introverted and reacts only to direct attacks or physical contact. One can even damage her slightly without startling her. Unlike the sitting Witches, she does not seem to be alerted more readily by flashlights.

The Wandering Witch remains as vulnerable as ever to cr0wning from a shotgun, and her more placid nature makes her much easier to cr0wn.

In Left 4 Dead 2's Hard Rain campaign, a large number of Wandering Witches have infested an abandoned sugar mill, which the Survivors must traverse to obtain fuel for their rescue boat. An achievement, Sob Story, is earned for navigating the sugar mill without startling any of them.

She has on occasions been observed to peacefully follow the Survivors without any provocation, although they may just be walking along its programmed path.

• The Wandering Witch's music cue.

Known Infected Individuals

• Carolyn (Zoey's mother): Turned into common infected minutes after being bitten.
• Jimmy Gibbs Junior : Turned into common infected (period of time unknown).
• Lt. Mora : Turned after a few minutes, he was in transition of turning and was still able to hold a gun and speak some English; however, he sees survivors as monsters (might not have been completely turned).
  
• News Chopper 5 Pilot : Turned into Common Infected in mid-air after rescuing and encountering the Survivors. He was bitten prior to rescuing the Survivors, which resulted in Zoey shooting him as soon as he turned.
• Sandra : Turns into a Common Infected (period of time unknown).
• The Church Guy : turns into a Special Infected (Boomer, Hunter or a Smoker) after one hour of being bitten.
• Helicopter Pilot (Left 4 Dead 2): Turned into Common Infected in mid-air after rescuing the Survivors, which caused Nick to shoot him.

Cut Infected

The Screamer

Main article: Screamer

Originally, there was going to be a Special Infected named The Screamer. Wearing a straitjacket, he would run from Survivors, hide, then let out a scream attracting the Horde; but he was removed because game testers found it too difficult to locate and kill him before he could summon a Horde, and his ability was given to the Boomer's bile instead. However, in Left 4 Dead 2, there exists a type of Uncommon Infected called the Clown which can attract a small Horde of idle Common Infected around him with his squeaky shoes. In the Passing, there is a new Uncommon Infected referred to as the Fallen Survivor. When shot, the Fallen Survivor attempts to run away, much like what the producers had planned for the Screamer.

The Leaker

A Special Infected called "The Leaker" was being developed. It had similar attacks as the Spitter and Boomer, and the ability to plant itself in the ground and act as a mine bomb. It was removed because the Survivors could run away from it, as the Leaker would alert the Survivors that it was planting itself. But, It is still possible to play as The Leaker with console commands by using "Map MAPNAME Versus", then typing in console "Boomer_Leaker_Chance" and a number between 0 and 1. You will know when you are a leaker if it says "You are a/the Leaker!", or if you explode on death and cause a small fire.

Behind the Scenes

• The idea of fighting massive hordes of melee-only Infected originated from a quick mini-game Turtle Rock Studios made while programming their Counter-Strike Source bots. The bots had knives, while the players had SMGs to fight them off with.
• In the Left 4 Dead (left4dead) and Left 4 Dead 2 (left4dead2 and left4dead2_dlc3) sound files, there are some sounds similar to a dog. All of them seem to have been cut, but they still exist in the game files. The attack sounds for "zombiedog" were recycled for the Hunter when he'd attack with his claws. This could explain why the Hunter yelps like a dog when he is killed. According to some of the Church Guy's "combatcolor" sound files, the "dog" sounds seem to have been re-made for when he would turn into a Hunter.

Notes

• All Special Infected except Tanks and Witches take 4 times damage when head shot by any weapon excluding shotguns.
• It is still unclear who actually gave the Infected their names in-game. It was probably some external faction, as the Survivors from both games use the same names for them after initial encounters. Possible candidates include CEDA, the military, the media, an unrevealed faction, or even various Survivors, though it seems unlikely that the military would have given them these names because in the comic, the two guard soldiers ask if "the whiskey deltas are changing," suggesting they've never seen a special infected before.
• Some of the names of the Special Infected, if not all, seem to have been assigned to them by CEDA or the government, and not by the Survivors themselves. For example, in Left 4 Dead 2, there is a poster early on in the Dead Center campaign with photos labeled "Boomer," and on the side of Bile bombs there is a label stating that the jar contains "Boomer Excretion." When Rochelle speaks of Smokers, she says that they were called Smokers on the news. Witches are also referred to by name on a safe room wall in Hard Rain, stating that the Sugar Mill is "full of Witches". Also, when exiting the Sugar Mill safe room, the building opposite to it has a banner hanging from the roof with the text "Stay away, Witches!" Additionally, in The Passing, one of the graffiti remarks on a pre-infection piece, stating one of the prostitutes in an establishment had "become a Boomer."
  • These could also be cases of official sources catching onto and using more well-known epithets for the Special Infected; as the aforementioned examples are all from the second game, which takes place three weeks after the initial Infection.
• Almost every Infected and deceased being in the game appears to have faded textures in comparison to the colorfully textured Survivors. This is probably to help prevent cases of mistaken identity between Survivors and Infected. It could also mean that the Infected are slowly dying, since a very sickly person can look pale, and dead bodies will lose color as the blood circulation stops.
• At the Bridge finale in Left 4 Dead 2, if the player listens to the military conversation on the radio long enough, the pilot mentions seeing flashes on the west bank (i.e. the side with the Survivors on it). The other soldier asks if it was the Survivors or "Whiskey Delta" to which the pilot is unsure. Whiskey Delta is the term the military use for the Infected, though they also use the term Infected when they questioned the Survivors if they are immune. One of the possible responses is or along the lines of "Hell yeah we've fought zombies!", which they accept as the Infected, meaning they understand that the Survivors refer to the Infected as such.
  • It is fairly common knowledge that the military creates initials and acronyms out of the names of their enemies, then uses words that begin with the same letters. The most prominently known example would be Victor Charlie (from the ICAO spelling alphabet) which has the initial V.C. That, of course, refers to the Viet Cong during the Vietnam War; therefore, "Whiskey Delta" could be used to represent "Walking (or Wandering) Dead" i.e. Infected.
    • This is highly confirmed by looking at the French version of the game: the military refers to Infected as "Mac Victor", M.V. being the initials of "Mort Vivant", the French translation of "Living Dead".
    • This is confirmed in Part Two of The Sacrifice comic, where one of the army men confirms that Whiskey Delta means "Walking Dead."
• The Infected seem to have become much stronger in Left 4 Dead 2. For example, in normal gameplay, the Boomer stumbles much less when melee'd than in the first game, and on Versus mode, as a Special Infected, you can kill a Common Infected with one claw attack as opposed to the first game, where it took several claw attacks to kill a single Common Infected. .
• The Special Infected that appear in Left 4 Dead have mutated further in Left 4 Dead 2 since the Infection has spread further and possibly advanced. This is shown as the Smoker now has multiple tongues, the Tank has more muscles and less hair and the Boomer appears gorier. Also, the Hunter appears to have more boils and lesions than in the first game, as well as seemingly having clawed off much of its clothing.
• It appears that most of the Special Infected have some form of intelligence. Smokers and Spitters will often run when sighted, hinting at a sense of self-preservation or at least the knowledge that their attacks must recharge. Boomers and Hunters will often hide before attacking, but the Charger will just run straight into the Survivors without much intelligence or thought into attacking. A very important aspect of this is that most Special Infected ignore pipe bombs, car alarms, and other noticeable events.
• The Special Infected in Left 4 Dead 2 seem to appear in duos, such as two Hunters/Boomers etc. during Crescendo Events such as the Mall Crescendo and the Barns Crescendo, as well as in finales.
• The Jockey is the only Special Infected to have one melee attack animation in both first and third-person. The Spitter has multiple third-person attack animations, and the Charger has two first-person animations.
• In Left 4 Dead, when in Versus, it takes many hits to kill Common Infected as a Special Infected (not counting the Tank). In Left 4 Dead 2, one hit from a player will kill them. This change is most likely due to the inclusion of the Bile Bomb, and its intended function as a method to get the Infected to fight and kill each other wouldn't be very effective if they did very little damage to each other. It could also just show that the Special Infected are gaining strength at a rapid rate.
• The Infected don't really seem to have a "method" of infecting others, though this may depend on the Survivor's immunity; some Infected (like the Tank) seem to be built for killing rather than infecting. None of the Infected attacks the player with actions that could transmit the Infection to them, disregarding the Hunter's bite. It is also unclear whether what the Infected can project (ex. Boomer bile or Spitter goo) is actually infectious, or perhaps it is up to the Common Infected to infect people while the Special Infected kill.
• All of the Special Infected (excluding The Tank where the only way to see his arm is by using the melee attack) are able to see their arms in first-person view. But most of them shouldn't, as they hold their arms in third-person view down or out of passive sight. Only the Charger and the Jockey hold their arms higher to see them.
• The use of orange/yellow filtering for first-person view for the Special Infected could have been inspired by the effects used to depict the the world through the eyes of the Infected in the film 28 Weeks Later, in which a similar orange/yellow filter effect was first used.
• The spawn "rules" for human-controlled Infected seem to be flawed. Although you cannot spawn where the Survivors can see you, this seems to be based more on the field of vision of the Infected than the Survivors. For example, if you attempt to spawn behind a small pole or other object that is narrower than your body (especially for the Boomer), even though in your view you cannot see the Survivors, they may be able to see you spawn.
• "The Passing" campaign drastically changes the way Versus is done (on all campaigns) when there are less than eight players. If there are less than four Special Infected on a team, AI-controlled Special Infected will constantly rotate and spawn during Versus to ensure there are always four Special Infected.
• Despite being able to fall from very high distances and react oblivious to it, in certain dying animations, Common Infected will seem to notice where they have been shot. For example, if an Infected has been shot in the abdomen, they may put their hands near the wound, then die. This implies that they do feel and recognize pain, but do not seem to show it, as if the Infection has destroyed specific nerves in the body and weakened others. Also, when Infected are shot, but not enough to die (e.g. by a pistol), they will act dazed for about a second, then continue attacking.
• Oddly enough, there are no Infected animals. The closest thing to one are the dead cows found around certain campaigns in both games, such as Blood Harvest. (Though in the sound folder for Left 4 Dead 2 [Sound/Player/Pz/Voice/Attack] there are sound clips labeled "zombiedog_attack", meaning there could have been Infected dogs in gameplay, but just later cut).
• Human-controlled Infected can revive incapacitated Survivors through use of the same button that a Survivor would use; however, this doesn't work in Left 4 Dead 2. If reviving a Survivor in Left 4 Dead while playing as Infected, it will say "Helping your friend up."
• In Versus Mode, while playing as the Jockey in first person view, he seems to be as tall as the other Infected, but the Jockey is the shortest of the Infected.
• There have been three Mutations that gives attention to some Special Infected. TAAAAANK! has all Infected players in Versus play as a Tank only, but with half the usual health in order to give the Survivors a small chance (3000 instead of 6000). Hunting Party is a Campaign Mutation where the only Special Infected that spawn is the Hunter. Riding My Survivors is when the Special Infected are Jockeys.
• Unlike the Common Infected, Special Infected do not lose body parts, even if you use a Chainsaw or a Pipe Bomb.
  • The only exception is the Boomer, which will lose his/her entire upper part of body upon death.
• Survivors will often refer the Infected as "it", implying that they no longer view them as human, although this may simply designed so Survivors can call out the Infected without claiming the latter's gender.

References

The Infected
Playable
Introduced in Left 4 Dead				Introduced in Left 4 Dead 2
The Boomer	The Hunter	The Smoker	The Tank	The Charger	The Jockey	The Spitter
Non-Playable
Introduced in Left 4 Dead				Introduced in Left 4 Dead 2		Cut Infected
The Witch		Common Infected		Uncommon Infected		The Screamer