Regurgitator

The Regurgitator is a boss zombie found first on early levels, and is the weakest major boss. It attacks by either swinging its massive arms at nearby players or spitting acidic bile and Puke Worms, hence the name Regurgitator. The number of Puke Worms increases as the player progresses, but resets upon the Regurgitator becoming Elite, Savage, or Savage Elite.

When defeated, the Regurgitator releases a massive swarm of Puke Worms. When the Regurgitator is at low health, it's recommended to reload your ammo so you can deal with the worms. Avoid getting too close as the Regurgitator's melee attack is far stronger than the Puke Worms. This boss is partially resistant to chemical weapons but is pretty weak against anything else.

The Puke Worms are tougher than Bloater worms and can swarm players easily, so be wary of them. The Regurgitator(s) usually complement tougher bosses. Beware of Savage Regurgitators in Nightmare Mode, as their buffed worms can easily wipe out an entire team of level 35-50s.

Also be aware of the bile acid it pukes out. Stepping in it could take a chunk of your health out, while bile acid from a Savage Regurgitator can kill you in seconds. However, the acid effect only takes place while you are standing in the acid, meaning you're safe as soon as you get out of it.

Trivia

 * The Regurgitator's default appearance is an infected surgeon, possibly contracting a stronger strain of the Bloater part of the Virus.
 * Puke Worms appear in the mission VIP. When you destroy the aquarium, a group of Puke Worms will come out. In Nightmare mode, these Puke Worms may be Nightmarish.
 * If you get puked on, you take damage.
 * There used to be a glitch where the regular Regurgitator's puke didn't damage you when you stepped on it, so it was as if the Savage Regurgitator had a special ability. This was fixed in an update.
 * After engaging a Regurgitator for a long time, the Regurgitator's puking will eventually cease spawning Puke Worms.
 * The Regurgitator is similar to the Boomer From Left For Dead. They are both extremely bloated, have low health for their zombie type, and spit bile.