Demons that live inside zippers.
Zippers are creatures that serve either angels or demons and are almost imortal, being able to regenerate fatal injuries even if their bodies get dismembered. However, Zippers enter a paralysis state if they get unzipped. Besides that, Zippers have a demon-like person living inside their heads, and seem to not be aware of them, as when Zipper first discovered the person living in his head, he was startled and tried getting rid of him. Zippers and their inhabitants are able to live without one another, as seen when Chuck and his demon-person were stuck in a microwave in the episode "Chuck to the Future".