In Left 4 Dead, there are six kinds of zombies, each with their attributes that make them unique. You've got to know the strengths and weaknesses of each, or you will find yourself dying in no time flat. Thankfully, we've got some handy-dandy zombie identification tips for you, and strategies for handling everything from a single common Infected to the player-killing crimes-against-nature that are Witches.
Gallery: Left 4 Dead
Appearance: The full gamut of human fashion. Hipsters, businessmen, pilots, cops, construction workers, nurses, and hospital patients are only a few of the different kinds of common Infected. However, they all share one thing in common: besides the caked blood and savage appearance, they are all relatively human-looking.
Sounds: Common Infected sound much like the infected humans in 28 Days Later. They snarl, scream, and vomit. When running at you, they will scream loudly and randomly, which is a pretty good indication that they are nearby.
Strengths: Common Infected are much, much, much faster than you are. They also come in the group variety more often than not, meaning that you will always be fighting several of these guys at once when the bullets start flying.
Weaknesses: The common Infected is about as durable as a 1000-year old vase. Two to three bullets from the pistol to the torso is normally enough to take them down, and a single shot to the head is an instant kill. They fall like flies to the advanced weapons like the semi-automatic shotgun, hunting rifle, and assault rifle. They also can't hear at all, allowing you to sneak up on them and bash them in the back for an instant kill. If you have ever played Halo, you know how this mechanic works. However, your flashlight must be off and you must be walking or crouched.
Special: Common Infected appear on the map due to two reasons: they spawned there when the map started, or the director summoned a Horde. The Horde is one of the nastiest challenges in the game due to its ability to catch you at a completely bad time. If the AI director thinks you are going too slow or just happens to feel like it, a large group of zombies will spawn somewhere nearby and make their way to you. It can be directly in front of you, to the side, or above. No direction is safe. On the harder difficulties, trying to face a Horde in the open without a pipe bomb is almost guaranteed suicide due to their speed, flanking, and high damage output.
Appearance: An extremely bloated fat man. Huge tumor-like protrusions come out of his face, and his belly button has a large leech-like thing that causes it to ooze blood.
Sounds: A Boomer is one of the loudest Infected in the game, but paradoxically, can be the hardest to recognize. This is because most of his vocalizations are similar to those of regular idle zombies. If they get louder, though, you know you've got a boomer nearby. He makes a vile retching sound when vomiting bile on the players.
Strengths: The Boomer is one of the nastiest infected due to his ability to spawn a Horde. Any player that is vomited on by this abomination will cause the AI director to instantly spawn a Horde of zombies that will chase them (and them alone) down and rip them to shreds. On top of this, any environmental zombies will be attracted as well, adding to the body count. If more players are affected, more zombies are spawned, but with diminishing returns. In other words, four bile-covered players don't spawn four times as many zombies in the Horde. His death explosion also covers players in bile.
Weaknesses: The Boomer is one of the weakest Infected in the game due to his lack of any combat ability whatsoever. His melee attack is ineffectual, he is slow, and falls from tall heights will kill him. He also dies after a single shot, which makes him explode violently due to being so fat and full of gross zombie fluids.
Special: The Boomer will hide around corners, behind pillars, and generally in locations where it is hard to hit him without him barfing on you. If you know where the Boomer is, bash him twice (not three times, or he will explode on you!) so that he stumbles backwards, back up, and blow him away.
Appearance: A hoodie-covered Infected that hunches down on all fours. The Hunter also slouches when not charging their pounce, making them appear quite a bit like urban punks. This is accentuated by the duct-tape wrapped around random limbs.
Sounds: A Hunter is instantly recognizable due to the screaming sound he makes when leaping. Outside of this, they growl and snarl frequently when meandering about, although it can be hard to hear sometimes. When attacking, the claws make deep rending noises and the victim will scream for help.
Strengths: Hunters are incredibly fast, have a low profile, and can strike from virtually any angle. This makes them one of the hardest Infected to hit unless their weakness is being exploited. They can't be removed from a player that has been pounced on without outside interference. In other words, the player that has been pounced is helpless. They also take a reasonable (but not incredible) amount of damage to kill.
Weaknesses: The delay after a Hunter's leap lets players shoot or stun them, making them much easier to kill. When pounced on a player, they take a moment to begin clawing at them, which also leaves them open to attacks or stuns. Finally, a stun will instantly stop whatever the Hunter is doing (even in mid-leap) and cause them to stumble for a few seconds, leaving them very wide-open.
Special: Hunters are nasty Infected and can ruin any player that is on their own, as they can tear the player apart before the teammates get there. However, if the whole team is in a group, Hunters are a piece of cake. Bashing them off the player they are tearing to shreds is advisable, as stray rounds can (and will) hurt the downed player. Hunters have caused more failed levels than any other Infected, as they will often pounce the last member of a team as they try to save teammates and incapacitate them quickly.