Bile Bomb

"Puke in the hole!"

- 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 weapon which appears in Left 4 Dead 2. The weapon was first mentioned in the achievement list. The Bile bomb is a throwable glass jar containing green Boomer bile. When thrown, it sends the Infected horde to wherever it hits, acting as a bait for 20 seconds, and potentially causing "friendly-fire" by leading the Horde to attack any Infected coated in the bile. When a Bile bomb hits any type of Infected, Survivors will be able to see the affected Infected's aura outlined in bright purple. 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 uses the same inventory slot as the Pipe Bomb and the Molotov Cocktail, 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 Common or Uncommon Infected will mostly ignore the Survivors so long as the bile is still in effect and they are not in the way, 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 down 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―however, Survivors must be careful, as some of the Common Infected might survive and attack the Survivors, making this tactic especially dangerous on Expert and Realism unless multiple Bile Bombs happen to be lying around such as the Burger Tank restaurant during Hard Rain. If the Tank is AI-controlled and bile is applied to other Infected, the Tank will ignore the Survivors and instead focus on attacking the Infected covered in bile, which can also buy the Survivors some time and cut down on the threat of other Infected attacking with the Tank.

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. 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.

Unlike the Pipe Bomb, the Bile bomb should not be used to lure Common Infected away from Survivors soaked in Boomer bile, as it will not do anything unless the Bile bomb hits any Infected; the AI Infected prioritizes Boomer bile-soaked Survivors over that of the Bile bomb.

Official Description
Give the infected a taste of their own medicine with this CEDA-developed gastrointestinal projectile. Any zombie you soak with this puke grenade will be swarmed by common infected.

Tactics

 * Even though the Bile bomb is designed to make Infected attack each other, it can also be used as a distraction. Use it during Crescendo Events or finales to reach the escape vehicle to make the Special Infected the only threat when one is thrown. However, this means that you must manually kill the infected, which a Pipe Bomb does on its own.
 * It can also be used for speed-runs through a chapter in the following ways:
 * By throwing the bile inside the safe room then closing the door, the ensuing Common Infected will attempt to attack the safe room door to destroy it. As safe room doors can only be destroyed by a Tank (which is not lured by them), they will be stuck attacking the door. This results in little to no Common Infected as the current Commons are busy attacking the safe room door.
 * You can throw it off an area the team will most likely not visit and run through the hordes of Infected as they surge to that spot. Make sure everyone is ready to go before you do so.
 * Players should be wary of Special Infected spawning as they are not affected by the bile like Common Infected, especially for Tanks when doing a speed-run as it can create an unexpected and sudden fight.
 * When thrown at Special Infected, it will result in both of them fighting each other. This is rather rare as they are usually not bunched together and spawn in various areas to attack the Survivors from.
 * Be wary of using Bile bombs during "Hard Rain", as it will spawn Worker Infected. Unless other Common Infected are hit by the bomb, they will ignore its effects and head straight for the Survivors instead, which can be dangerous on Expert and Realism modes.
 * A Bile bomb should be used on a horde only if you anticipate one coming or the team is in critical condition.
 * Bile bombs are very rare to find during "Dark Carnival" and "The Parish". In "Dark Carnival", they only appear during "The Highway" and "The Concert" (one always spawns in this chapter), and for the latter during "The Park" and "The Quarter". Teams should have one player carry a Bile bomb to be used during Crescendo Events or finales.
 * Note that in "No Mercy" the only way to obtain a bile bomb is to kill the CEDA Worker Infected that spawns near the end of "The Sewer" and "the hospital", since the bile bomb does not have a chance show up in the entire campaign.
 * Bile bombs are much more effective in Versus than in Campaign Mode. As the Special Infected are now controlled by players, hitting them with a Bile bomb blinds them temporarily and allows the horde to attack and slow them down. This works well on Tank players who will struggle to get the Common Infected out of the way unless aided by a tactical Boomer.
 * They are useful on "The Hotel" and "The Bridge", as Common Infected will still chase after them and fall to their deaths, allowing the players to progress with ease.
 * With practice, players can kill or make Witches retreat if a Bile bomb is thrown from a long distance. When used against the Tank, it will not trigger the fight and will deplete most if not all of his health, making the fight against him easier.
 * Unlike Molotovs and Pipe bombs which bounce off surfaces, once a Bile bomb is thrown it will shatter when it reaches a surface or wall. Be wary of how you throw it as improper throwing may waste the bomb.
 * Do not block incoming Infected as they run towards the impact zone. This will result in them stopping and attacking you because you are blocking their way, similar to blocking a Witch when she is chasing after the startler or retreating.
 * When facing a startled Witch, do not use Bile bombs against her. She will be too fast for the Horde to catch up, decimate them with ease and result in her targeting the thrower if hit by one. It does not slow her speed down either so use a Molotov instead for this purpose.
 * If one manages to throw a Bile bomb and then throw a Molotov where the Bile Bomb lands, the infected will walk right in the fire, saving the needed ammo to kill them. However, it's a lot more effective to use just a Pipe Bomb or a Grenade Launcher.
 * The Bile bomb becomes more dangerous to use the higher the difficulty is. As hordes become stronger in Advanced and Expert, be wary of when to throw it: it can lead to the team being inconvenienced since it will spawn a horde even if there isn't one.
 * This is especially important against Tanks - if the team is already taking a while to kill the Tank, tossing a Bile bomb to coat the Tank may just lead to the Survivors needing to fight an angry, damaging horde and the Tank once its effect expires.
 * The Bile bomb is a mix of both the Pipe bomb and Molotov. It has the area effect of the Molotov while using the attention grabbing mechanics of the Pipe bomb.
 * This can be used with explosive or incendiary items to kill all the Infected in one go.
 * It can also be used with the Grenade Launcher for "Dismemberment Plan" or with the M60 for "Til It Goes Click" achievements.