The Boomer

The Boomer is an extremely bloated Special Infected, whose inflation seems to be filled with an odorous slime. They are able to vomit bile; if it hits the Survivors, it covers them, temporarily blinding them and attracting the horde. When the Boomer dies, it explodes and discharges large amounts of gore and viscera, which will also attract the Common Infected if an unfortunate Survivor is caught in the blast. In addition, both Infected and Survivors are knocked over by it; this could be used to get a Hunter off of a pinned survivor who is stuck on a ledge and out of range.

Boomers are relatively delicate, as far as the Special Infected go; this means it is only able to take a very small number of bullets before it bursts. If Boomers drop from a particularly high place, such as from a roof top into a street, they "pop", which is an effective means of ambushing Survivors. However, the Boomer does not burst when falling from tall heights in Versus.

In Versus mode, players are able to play as Boomers. Their ability to vomit is gauged by a somewhat slow-filling meter, which was probably employed to balance gameplay. Though the Boomer is clearly not one for combat, its melee attack can deal double the damage of a regular Infected, much like the other boss Infected. It's recommended to begin hitting Survivors if you've already vomited on one or more. If they aren't careful, it's possible that they will cause the player to burst, covering any clean Survivors left. Only one Boomer is allowed while on the Infected team in Versus.

Extent of Mutations
The Boomer has been heavily mutated by a strain of The Infection. It has become extremely bloated to the point that a slight rupture in its flesh will cause it to explode, sending the bile, blood, and other contents of its body everywhere. This is due to the infection creating large amounts of specialized bile to build up within its body under high pressure. Massive growths have appeared along its skin, indicating that it may still be expanding. It has developed the ability to project its vomit great distances, and this bile has developed the unique characteristic of attracting hordes of Infected, by releasing possibly what could be called a specialized hormone on contact with human flesh. The Bile bomb however, can also attract The Horde to any infected. Though its mentality is similar to that of the typical Infected, it is not distracted by such things as the flashing lights of the Pipe bomb, nor is it apparently attracted by Crescendo Events. This could indicate that it has some form of intelligence, and is focused on keeping the Common Infected concentrated on potential victims.

The Boomer reappears in Left 4 Dead 2. It has a new skin, as well as a few new sound effects, but it's role is essentially the same. A major change to the Boomers in Left 4 Dead 2 is the addition of a female Boomer.

The Female Boomer (As seen in video below) is the same as her male counter-part, and the differences between the two are merely cosmetic. She is seen wearing a dark blue or black tank top drenched in bile, and shorts. Unlike the male Boomer, she doesn't have boils or growths. Instead, her skin folds forming flabs and perhaps highly infected forms of tinea on the backs of her legs. Her teeth seem to be horribly malformed possibly meaning the virus or the bile can damage the enamel and form cavities.

500px|left|Female Boomer

Survivors
General:


 * Listen for the heavy breathing, gagging and burping sounds.
 * Keep an eye out for defensive positions, that way you'll be ready if the Boomer blinds you.
 * Avoid being too bunched up with the other Survivors. There's no sense in all four of you getting puked on at once.
 * On expert, finding and killing the Boomer before he can vomit or explode is incredibly crucial as the Boomer bile attracts the horde, which on expert difficulty is much more dangerous than any other difficulty.
 * On expert, Boomers will often claw Survivors they have vomited on, dealing even more damage.

Before bile spit or Boomer death explosion:
 * If the Boomer is too close, it's a good idea to hit it with your melee attack (which will push it back to some degree) then back away to a safe distance before shooting or you'll get covered in bile, even though you weren't vomited on.
 * CAUTION: You can only safely push a Boomer back about three to four times, if the Boomer has full health.)
 * Only if the Boomer is sufficiently far away from both yourself AND all other Survivors should you shoot it.

After being vomited on:
 * Hiding behind something or running away when it's vomiting makes it harmless for some time and may even force it to rush at you clawing.
 * Know that a massive horde will immediately descend upon you (and any others who have been slimed).
 * Hold your fire! Since you can't see, friendly fire is the most likely result. You need to:
 * Run to a defensive position (corners and doorways are particularly good).
 * Crouch! Other Survivors will be able to shoot over you safely if you do so.
 * Use melee continuously to survive the incoming zombie horde.
 * Once your sight starts to clear, mop up with your weapon.

Helping a slimed Survivor:
 * Stay close to the stricken Survivor.
 * Help melee the horde back or shoot if the blinded Survivor stays safely crouched.
 * Help the stricken player to safely get to a corner or high ground to protect him from the Horde.
 * Throw a pipe bomb to distract the horde.

Infected
While it may be difficult to be completely stealthy as a Boomer, try to hide in shadows, around corners, or within hordes of Common Infected. To ensure that you slime the Survivors, vomit on them at close range, then run up to attack them so that they will be more likely to shoot you. You will explode and spread the bile within a certain radius around you. Once you cover a Survivor in slime by either of the two ways, the Survivor(s) will appear with a bright purple outline replacing the original one indicating health status.

Your best teammates are the Special Infected.


 * First and foremost, the Boomer can only spawn one wave of Infected per Survivor at a time. Vomiting on a Survivor and then exploding on the same Survivor will not generate additional Infected despite getting one person "twice". To generate additional Infected, you must either explode on a "non-purple" Survivor, or wait until all Survivors are no longer surrounded by a purple aura with bile and then strike again. Therefore; he who pukes and runs away, lives to puke another day. The best tactic for this is the "ninja-boom". If it is possible for you to run away after you vomit on the players then run to hide. Hide farther down the level and wait for your vomit to recharge. Once it has, initiate the same attack - vomit and run.


 * Boomers are large, making them easy targets. If you manage to slime a group of Survivors in a place where running away is going to be difficult, and finding cover will take some time, don't be afraid of running in and clawing them, as this will deal extra damage. While in the middle of the chaos, it can also confuse the Survivors from which direction the horde are actually attacking them from. Also, if they're not careful, they can shoot you once they're clean, resulting in being covered again.
 * However, often it is more effective to back off and find a place to sit and let your bile recharge, as some horde attacks can take up the full extent of your recharge time. If you're lucky and have good positioning (ideally sitting in a window above the group before they emerge from a doorway below), you can score multiple horde attacks by raining bile down upon them each time they emerge after the horde, causing them to have to huddle back inside, depleting their health, and giving your teammates ample time to respawn and deal damage.
 * Since the Boomer has a very distinctive gurgling noise, choosing a good spawn-time is crucial. Do not spawn when the Survivors are far away and attempt to rush them, especially in the open. Even if you are hiding, the Boomer's gurgling will alert the Survivors of your presence. If you spawn inside a room only a second before the Survivors pass the room's door (make sure the door is open/has a hole in it), you can do a spawn-vomit succession without giving them time to react. If you don't manage to cover all of the Survivors, you can either run at them clawing, hoping to explode in their face, or escape and return later.
 * The Hunter can pounce on the Survivor covered in bile to add terrible confusion to the mess; the bile will summon the Infected, who will create a meat shield for the Hunter. By the time the other Survivors are able to get to their pinned friend, it may be too late.
 * Boomers have a small amount of time in which the survivors may avoid being slimed even when you have thrown your bile. A tactic used is to have any other special infected team up with you (as long as it is not a tank) and hide around the corner ahead of the survivors. The survivors will soon cross by and when they are close enough have the boomer throw up while the other scratch the boomer out to the open. In doing so the delay of the boomer bile has been reduced to nearly nothing as the survivors face off the incoming horde.
 * On the other hand, a Boomer can vomit on a Survivor who has been pinned by a Hunter to call the horde, and then hide from the rescue party or stay and attack, heading to the clean Survivors to cover them when they get close to melee your labor away.
 * If you are playing a Hunter and a Boomer vomits/explodes on the Survivors, they will often huddle up in a corner "spamming melee". This has upset a lot of Hunters who cannot pounce through this wall of melee. The March 25th update added a melee "fatigue" of sorts in Versus mode, but it is not reliable to plan an attack. However, if you, the Hunter, pounce into the top of that corner instead (pounce over the Survivors heads), you will land on a Survivor and his teammates' melee will not hit you. As they are blind, they will have a hard time finding you inside their huddle. This can, in teams who do not communicate well, cause death to a player. Since the Survivors are blind, 2 or 3 Hunters can perform this plunge into the walls top corner without being afraid of getting shot.
 * The Smoker can constrict a Survivor who has been covered, effectively creating a piñata for the Common Infected. This is a very effective way to incapacitate a Survivor quickly.
 * The Tank can distract those who are not covered in bile, cutting them off from helping their friend. It can also incapacitate a covered Survivor, rendering them nearly helpless against the zombie onslaught all over them and adding the chance that they'll bleed to death.
 * During Tank attacks, take the opportunity to vomit on the Survivors. This is a particularly helpful and effective action, as the horde sticks Survivors in place, and forces them to deal not only with a Tank, but dozens of zombies. Often getting a well-placed vomit attack in during a Tank attack spells death for the Survivor team.
 * While a Survivor is covered in bile, they cannot see the outlines of the other Survivors (or that of the Hunter after a pounce). While another Infected is attacking a straggler, take the opportunity to cover the other Survivors with bile. While this may cause the Horde to spread out, it is important to impair the other Survivors' vision so that it becomes more difficult for them to work together and to aim.


 * The Boomer can hide next to cars with alarms and Witches to trick Survivors into shooting them. The nearby explosion will cause the alarm to be triggered or the Witch to be startled (if shot). However, after the new update, a dying Boomer's explosion will no longer startle the Witch.
 * Waiting behind doorways and in small rooms will guarantee at least one successful slime.
 * If you are stuck outdoors, hide in a place where the Survivors cannot see you and wait for them to be distracted by something else, then run in and vomit.
 * The Boomer is the only Infected class as which you should almost always attack an incapacitated Survivor. If you can, try to vomit on prone Survivors so that the Horde comes for them. This makes them almost impossible to rescue as every zombie hit interrupts a rescue attempt.
 * Vomit on Survivors pinned by Hunters or Smokers, unless the Survivors not pinned have low health, at which time it would be best to try to get them incapacitated.
 * Hunters are a great distraction and can let you close the distance without being noticed.


 * In areas with alleyways or other high roofs, jump down into the middle of the Survivors. You'll either be shot in surprise or get an excellent chance to vomit on all four Survivors in quick succession.
 * You can also stand on rooftops and vomit down on the Survivors. Gravity will help the bile to reach them even from great heights. If you explode in mid-air, your innards will rain down on Survivors as well (March 11th update).
 * Don't hide right next to thin walls. Not only can Survivors shoot through most of them, your ample mass may stick through (due to vector errors), giving them a free kill. The slime from the aftermath will, unfortunately, be unable to get through. Try to hide slightly off the wall to minimize cheap kills.
 * In relation to cheap kills, let a Hunter melee you four times before you charge a Survivor. If the Survivors then attempt to melee you, you will boom on them immediately. You could also set yourself on fire, and do the same thing, but fire can kill you very quickly. So you must be careful not to light yourself too soon, or too far from the Survivors.
 * When you pop, you knock everyone back. This includes, but is not limited to, Survivors, Common Infected, Hunters who have pounced on Survivors, Smokers constricting Survivors, Tanks and even the startled Witch, but for a short time. The good news is that you can knock Survivors off of high ledges; the bad news is that you can do the same thing to Tanks. Take care of where and when you explode!
 * Before the March 25th update, Boomer vomit could be blocked by other Infected. With the update installed, the Boomer's vomit can pass through them and hit the desired target successfully.
 * Try puking on incapacitated survivors for swift horde kills.
 * A tactic used by some players is to be in spawn mode, and rush forward while on a roof. When you are almost to the edge, you spawn, and then fly through the air. You will land near the unsuspecting survivors, and puke all over them. This is really only useful if you are on a rooftop a far way away from the survivors.
 * If you are a Hunter or Smoker, and the Boomer has puked on all but one survivor, try to attack that survivor, as his team-mates may not be able to see what you are doing, and this allows you to, at least, inflict huge damage before the other survivors notice you. If a Boomer has only vomited on a single survivor, you could organize your team to then pin the other three, leaving the single blinded survivor confused as he has to battle the horde alone, and even if he survives, the other infected on your team may have critically injured or killed the other survivors.
 * As a Boomer, you can put the Survivors into some extremely sadistic lose-lose situations. If you can, sneak up on a single incapacitated Survivor and simply stand right next to him or start clawing him. The incapacitated Survivor cannot do anything about your presence other than shoot you, which will cause him to be covered in bile, resulting in swift death. You can also so the same to a pinned Survivor, and if any of his friends try to shoot the Hunter or Smoker pinning him, they may hit you, causing a similar result (however, the Infected pinning them will be knocked off.) While these attacks are extremely cruel and funny, it is advised that you vomit before-hand, just to make sure that your plan doesn't backfire.
 * Your presence alone is a weapon. If the Survivors are caught up battling a horde or multiple Special Infected, you can wander out and simply hang around near the Survivors. Make sure you are close enough so that if you explode you'll hit at least one Survivor, and that you are far enough away to avoid being punched. If they panic and shoot you, they'll get slimed. If they run up to punch you back, you can puke on them, and they'll get slimed. Either way, they'll get slimed.
 * Remember, that a Boomer has no pinning attacks, meaning that even with a full team of Infected, you can't all pin a full team of Survivors, leading to instant survivor failure. You must, instead, try to have your horde incapacitate at least one Survivor, allowing your Infected allies to sneak in and get all the other Survivors while the single incapacitated Survivor is helplessly pounded by the horde you summoned.
 * Smart players in Versus will stand by incapacitated Survivors while a teammate is attacking as a Tank. The incapacitated player is forced to shoot the Boomer and get puke on them, attracting the Horde and most likely finishing them off. Or the player will continue to melee the play to dwindle their health. As long as no other Survivors are around to melee you away, you get points for the melees and Horde attacks.

Boomer Tips and Tricks Gameplay
Here is a video with a lot of helpful information and tactics for the Boomer. Thanks to Criken for the video.

http://www.youtube.com/watch?v=rqc6p5KU06E&feature=channel

Behind the Scenes
In the developer's commentary, it's mentioned that originally the Boomer's explosion simply caused damage to nearby players, and that the horde-attracting abilities were assigned to the Screamer, another Special Infected that was cut from the final game. When the Screamer was dropped, the screams that formerly attracted the Horde were changed to the Boomer's bile.

A video of the original Boomer's behavior can be seen 27 seconds into this video: http://www.youtube.com/watch?v=7lg1U9FXzy4

When the Boomer's bile was first added to the game, it was red. It was replaced by the green seen in the final version.

Trivia

 * The Boomer was the first Special Infected ever conceived.


 * The Boomer is the only Infected that does not appear in the intro movie alive, although Bill is seen analyzing Boomer bile at the beginning. The recognizable "blown up" corpse of this Boomer can be seen to the left of the screen, against the wall.[[Image:Boomer corpse copy.jpg|thumb|195px|right|The Boomer corpse in the Intro Scene.]]


 * Bill gets a small sample of the bile on his fingertips and wipes it off on Francis, however this wasn't enough to attract a Horde until later. This may show that the bile in small amounts does not create enough of the horde attracting hormone to create a horde.


 * A well placed head-shot will cause a Boomer to die without exploding, but this is rare.


 * Oddly enough, even when killing a Boomer by shooting it in the foot, the Boomer still explodes, even though its upper body is the part that explodes


 * When the Boomer explodes or vomits, the bile does not appear on the ground. This fits in, because otherwise the horde would always be attracted to the site of a Boomer death. As it stands, the horde is only summoned when the bile comes into contact with a Survivor. It is possible that the Survivor's natural pheromones combined with the bile produces a scent that is strong enough to attract a horde of large size. Strangely in Left 4 Dead 2, when a Bile bomb is thrown, it attracts a horde, regardless of whether it hits an infected or not.


 * When the Boomer explodes, the arms disappear, possibly because they were blown to bits. If there was that much force in a Boomer's explosion, it would more than likely do at least some damage to the Survivors.


 * The Boomer's explosion is enough to break glass and destroy wooden doors but curiously still does not do damage to the survivors. This may be due to the liquid bile muffling the explosive impact into a mere concussive force.


 * Judging by the weight and immensity of the Boomer, its body should have been able to restrict the Boomer from jumping higher than a foot or climb ladders since the stress/tension would cause the Boomers' internals to strain and explode. However, for gameplay purposes, Boomers are given as much freedom as their Common Infected counterparts.


 * When examining the Boomer's navel, players can seen the Boomer's intestines protruding from it.


 * The Boomer can be killed by close combat weapons instantly in Left 4 Dead 2, although this is probably a very bad idea as the killer would get covered in Boomer bile from the explosion.


 * A Boomer was apparently hit by a police car at the beginning of Death Toll as a pair of Boomer legs are laying against the police car. This might be the reason for the large amount of dead bodies lying around the same area as if a horde were summoned.


 * As with the other playable Special Infected, human-controlled Infected can revive incapacitated Survivors through use of the same button that a Survivor would use.


 * A Boomer is seen hanging by his limbs in the Left 4 Dead 2 campaign, Swamp Fever. Whether this was done prior to becoming a full fledged Infected or not is debatable. This can be seen here: http://www.youtube.com/watch?v=2FyNc57Fsks at 0:14.


 * Although what looks like large, pus filled sacks are covering one of its eyes, it still has full vision as seen in Versus mode.


 * The Boomer, along with the Tank, is the only Special Infected to have noticeable changes to physical appearance upon dying. For example, the Boomer lower body only remains after exploding. In addition, the Tank's skin texture changes if it dies on fire. However, none of the other Special Infected undergoes form of physical changes upon death.
 * Boomers Bacteria. The Boomers music.


 * Along with the Witch, Jockey, Spitter, and Hunter from Left 4 Dead 2, the Boomer is not wearing shoes. Although he is wearing socks.


 * Although he doesn't have a major appearance in the Zombie Survival Guide, he has a minor appearance. He can be seen when Ellis is looking out the elevator window for about 2 seconds after they escaped into it.


 * The female Boomer is referred to as "Boomette" in its model files. Currently, the Boomer is the only Special Infected to have both female and male models.