The Infected

"I'll see peace back on earth if I've gotta murder everyone of these bastards with my own bare goddamn hands!" - Bill

The Infected are the "zombies" in Left 4 Dead. They are more akin to the zombies from 28 Days Later than to the more popular slow, shambling type. Instead of being dead, they are living humans who have been infected with a mutated virus. There are six varieties, four of which are playable. Five varieties are considered "Boss Infected" which have special abilities in addition to doing more damage against the Survivors. All AI-controlled Infected are procedurally spawned by the Director.

Common Infected
Common Infected are the most commonly-faced enemy and they are the easiest to defeat. They are completely AI-controlled and fairly weak. Their strength lies in the fact they attack in groups sometimes as large as several dozen, known as hordes. While they seem capable of ignoring pain, they can still be killed easily. They are capable of climbing ladders and scaling objects.

Hordes
Hordes are large groups of common Infected that will rush the Survivors at random intervals, after triggering a car alarm or other Panic Event, during a Finale and during the aftermath of a successful Boomer vomit attack.

The Witch


The Witch appears only once or twice per campaign, and is passive unless provoked by flashlights, gunfire, or Survivors getting too close. She is very powerful and is capable of killing players with a single attack as well as sustaining much damage before dying. While the Witch can be killed, it is best to avoid startling her unless absolutely necessary.

The Screamer


The Screamer is a cut unplayable Special Infected that would have appeared one or more times per map. It would wander around until it came in contact with the survivors. Once it saw them, it would quickly run away and hide. When it was successfully hidden, it would let out a scream that would attract the horde.

During testing, play testers complained that the Screamer would end up being too hard to spot in a crowd of infected. Its horde-attracting scream ended up evolving into the Boomer's vomit.

A sound file describing the screamer and a picture of the Screamer can be found in the Left 4 Dead Folder, by searching for screamer.vtf, and com-thescreamer.wav.

Zombie Dog
You can find it's sound files here's the guide /left4dead/left4dead/sounds/player/PZ/voice/ any folder it has all of the zombie dogs sounds.

The Boomer


The Boomer is an Infected that spits vomit at survivors, which blinds them and draws other infected to them. At a distance, the Boomer is little threat, since he is extremely slow. However, he can vomit on Survivors, attracting the Horde. When he dies, he explodes and covers any Survivors who are close enough in bile. If a Boomer is killed while close to a survivor, the player loses control for a few seconds and stumbles away from the now dead boomer.

The Hunter


The Hunter is extremely similar to the fast zombies from Half-Life 2, although far less charred. The Hunter is extremely quick and agile, and is capable of scaling walls. Additionally, he can pounce players and pin them down until killed or shoved off by another Survivor. Since this "class" is extremely agile, he is also physically weak and cannot take much gunfire.

The Smoker


The Smoker is an ambush class who can strangle Survivors with his long tongue, similar to Half-Life's Barnacle. The help of another survivor is required to escape from a Smoker's hold. As his name implies, Smokers can emit smoke to impair Survivors' vision and voice communication when in danger, or automatically when killed. The Smoker can drag players that he has captured with his tongue, towards himself. The smoker remains stationary and cannot move for a few seconds after having his tongue removed from his captive by another survivor.

The Tank


The Tank is the strongest of Special Infected. Although not as fast as a hunter, the tank can move as fast as a survivor at full health and has incredible strength and resistance. To counter this overwhelming advantage, the Tank has a frustration meter that goes up whenever the Survivors aren't in view. When the meter is fully depleted, the player loses control of the Tank. The Tank is capable of throwing large objects with sufficient force to momentaraly stun Survivors.