Pain state

A monster's pain chance refers to the probability of a monster being distracted from its attack when being attacked by the player or another monster. The monster, when in pain from being hit by a projectile, shot, clawed, punched, or chainsawed, halts its attack and restarts from the beginning, sometimes by trying to maneuver into a new position to attack its target. It may or may not give out a distinctive cry.

The chaingun is particularly useful against monsters with a high pain chance, as due to its rapid rate of fire each bullet causes the monster to cringe and restart (called "doing the chaingun cha-cha" in the original Doom manual). These include Imps, Demons, Lost Souls, Cacodemons, Pain Elementals, Mancubus, Arachnotrons and Revenants.

For those monsters with a low pain chance, the shotguns or plasma guns are preferred. Only the Player and Lost Soul have a 100% pain chance.