The vile spawn of the Putrid Defiler, pain worms gestate within the brain of a host monster, feeding off the demonic thoughts of the beast. If the monster is killed while the worms are gestating, the parasites eat their way through the beast's brain and ultimately burrow out of its skull in search of a new body to inhabit. It has be rumored that certain demon groups will simply imprison one of their brethren rather than risk killing the host and infecting another.