Bile Bomb

"Fight amongst yourselves!"

- Nick

"Here comes the Bile, you sons of bitches!"

- Ellis

The Bile Bomb (a.k.a. Boomer Bile, Vomit jar or simply puke) is a new weapon which appeared in Left 4 Dead 2. The weapon was first mentioned in the achievement list here. The Bile bomb is a throwable glass canister containing the unmistakable green Boomer bile. When thrown, it sends the Infected horde to wherever it hits, and potentially causing "friendly-fire" by leading the horde to attack any Infected coated in the bile. Bile bombs, overall, allow for a brief moment of rest and preparation during a battle.

The Bile bomb can often be found in the first two levels of Dead Center. It may also be dropped by CEDA Worker Infected, though this is less common. The Bile bomb will use the same inventory slot as the pipe bomb and the Molotov, so only one of the three can be carried at one time.

The bomb spreads Boomer bile on whatever it hits, and the horde summoned by the Survivors will attack whatever is covered in bile, including other Infected. If the Bile bomb is used on an empty space, it will summon a horde and all of the local Infected to the place where the bomb landed. Usually, the Director will spawn a horde if there are not a lot of Infected, and the Infected will ignore the Survivors so long as the bile is still in effect, making them easy targets. The Common Infected hit by the bomb will begin attacking each other, as well. The bomb can also help in Tank fights as it calls a horde to attack it. The effect of this is only marginal, however, and usually just serves to slow the Tank and damage it slightly rather than kill it. Sometimes, though, the Tank will be rendered immobile by the Common Infected hitting it. This can buy the Survivors a lot of valuable time―Survivors must be careful, some of the Common Infected might survive and attack the Survivors, this being especially dangerous on Expert and Realism.

The bomb can also be used to confuse Special Infected as it will make any two of them that have been hit to fight one another as well as the oncoming Common Infected. When a Bile bomb hits any type of Infected, Survivors will be able to see the affected Infected's aura outlined in bright purple. Throwing the Bile bomb on a Survivor will not draw a horde to attack; however, the horde will be drawn to the location where the bomb impacted, and will attack any Survivors within that impact area.

Tactics

 * Despite the intention of the Bile bomb as a way to get enemies to fight each other, a far better use for the Bile bomb is as a distraction during a crescendo event, or as a distraction while quickly running as far forward through the level as possible to find the next defensible location. If you leave common Infected far enough behind, they won't chase you.
 * If a horde is not present, the Bile Bomb will cause the Director to summon one. So It is better to use it when a horde is present, or at least when you know a horde will be coming soon.
 * Be warned that if vomited on by a Boomer, the attraction to you is far greater than that of the Bile bomb. So if you get covered in bile, don't bother wasting this grenade.
 * The Bile bomb is like a mixture of a pipe bomb and a Molotov. It has the horde-attracting power of a pipe bomb, but any Infected caught in the blast will get stuck with the bile, like if you were to be caught on fire with a Molotov. If it's a horde, you don't need hit them directly; rather you could attract them into one area. If it's a Tank, then hitting him directly counts.
 * Boomer Bile bombs also distract Infected for a longer time than Pipe bombs, making them potentially more useful for situations where the Survivors need to run from one point to another with Infected attacking, such as a Gauntlet Crescendo, a finale when the rescue vehicle arrives, or a gauntlet finale.
 * Bile bombs are much more useful in Hard Rain than in any other campaign. The Worker Infected will ignore Pipe bombs (due to their ear protection), but still chase Bile bombs. However, they ignore Bile bombs that don't hit any Infected due to the fact that the distracting effect used for bile that didn't hit any Infected uses the same programming as the pipe bomb, which Worker Infected are programmed to ignore. The Worker Infected will resume targeting the Survivors after the bile wears off or the covered Infected are killed.
 * It is usually more useful to use a Molotov on a Witch than a Bile Bomb. Bile bombs will not slow her down and the Infected that come to attack her will do little to stop her as she is faster, and they will attack you after. In most cases, a Witch will either incapacitate or kill her target or being killed by the Survivors before the horde arrived. It is, however, possible to throw a Bile Bomb from far away and not startle her, but this might be difficult to do.
 * The Bile bomb is considerably much more valuable than it already is while in Versus, where Infected are controlled by players and it confuses them more than if thrown on an Infected bot. Because they are blind and are unexpectedly being attacked by their own team (i.e., the Common Infected), they often panic, especially Tank players.
 * In the absence of a needed Pipe bomb or Molotov, one way to use the Bile bomb is to throw it on or near a propane tank, gas can, or oxygen tank. Wait for the Infected to swarm it, then shoot the object.
 * If in a high area, such as The Bridge or The Hotel, throw the bile off the side of the ledge. Infected will swarm off the edge and fall to their deaths. Pipe bombs also work with this strategy. This will not credit you with kills, though.
 * When throwing a Bile bomb to avoid hordes of Infected (like in the Parish bridge run or Dark Carnival gauntlet at the barns), do not shoot any Infected going for the bile as the Director will respawn killed Infected immediately. The Infected will gather around the bile emptying the area effectively if left alive.
 * Bile bombs are great to have while playing on Expert, due to the hordes being much more deadly, it's advised to throw it to the area that is unreachable to the survivors, for some reason this can prevent the common infected from spawning and "freeze" the common infected that already around, the area or route will be much safer to pass. This could make a difference from being wiped out and getting to safe room with little trouble.
 * It is wise to preserve bile in levels with Gauntlet Crescendos. Note that in Dark Carnival, it only spawns in the first and last map and, in the Parish, only in the second and fourth map. Teams should plan ahead for these events and have two players carry bile for these occasions.
 * The Bile bomb can be used to reduce or eliminate the number of Common and Uncommon Infected that you will encounter in a level greatly, up until the first Crescendo or panic event if it exists. If you throw a Bile jar into the safe room, close the door before any Infected get inside, and refrain from killing any Infected that attempt to enter the safe room, then a large group of them will indefinitely attack the door. Since the number of live Common and Uncommon Infected is limited by the Director, the rest of the level will contain few Infected or none at all. Thus, if this exploit is to be attempted, it is recommended that you kill any computer-controlled Survivors beforehand, or they will prevent the Infected from gathering at the safe room. This exploit only works on levels other than the first or finale of any campaign, and you will still encounter the Special Infected.
 * This exploit works in the Dark Carnival Finale. Throw the bile bomb in the safe room and run past all of the Infected that are not directly blocking your way (shoot a few if you have to). The computer-controlled survivors are apt to follow you rather than stopping to kill the infected and many infected will get stuck at the safe room door even if a few get shot.
 * The Bile Bomb also works well in conjunction with the Grenade Launcher, especially if the Infected in the area are too scattered to make efficient use of the launcher's blast. The bile will draw the Infected out into the open, and they will pack together, making them an easy target. This strategy can be employed to more easily earn the DISMEMBERMENT PLAN achievement.
 * The same can be used with the M60 on The Passing, as the bullets can penetrate multiple common Infected. It can also be used to get the achievement, TIL IT GOES CLICK.
 * The aura around Infected covered in Boomer bile will not appear in Realism mode. Hence, the only way to tell if one is covered in Boomer bile is to see the bile dripping off the Infected. Still, it is best to remember that the aura should not be relied on in Realism mode to spot any Infected affected by the Boomer bile effect.
 * In Versus modes, the Bile Bomb can be extremely useful against a Tank. The Tank will be slowed down by the horde, but more important, it will be blinded for a while. This will leave you a little time to retreat to a safer place, or simply time to shoot it while it can't see you, or lob a well-aimed Molotov that the Tank won't see coming. Also, you will see the pink outline of the Tank while it is covered in bile. If you face a Tank that likes to hide in the dark or in the storm, throwing rocks at you, while you cannot see it or aim at it, throw some bile at the source of the flying rocks. The Tank will then be clearly visible, and an easy target. It is inadvisable to use it on a Tank that is about to die, as it will summon a horde afterwards, causing more issues for the survivor team.
 * However, this tactic is not useful for cane field in The Sugar Mill, as you can easily lure the Tank to the second floor of the building with the elevator to fight with him, and throwing Bile Bombs in the cane field can possibly startle a witch.
 * Unlike Molotovs or Pipe bombs, Bile Bomb will explode on impact to any surface, including floor, wall, Infected, or any other Survivors. So it is advised to warn teammates not to run in front of you before throwing one. Despite the bile won't cover the Survivors, it will draw Common Infected near the Survivors, or even force the Survivors to leave a defensive spot.
 * Bile Bombs will NOT set off a Tank. You can toss a bile bomb on a Tank if you see part of its body and it will not trigger him to go after you. Depending on difficulty, the resulting horde will kill him.