Bile Bomb

The Bile bomb is a new weapon appearing in Left 4 Dead 2. The weapon was first mentioned in the new achievement list here. Not much is currently known about this weapon, except that it contains Boomer bile. Also, once you kill one of the Hazmat Infected, they should drop one of these containers full of bile. There's an achievement to pick up 10 of these containers after killing the Hazmat Infected. It will most likely take the place of the pipe bomb and the molotov.