Vile Ashes

Demons do not leave bones behind on death. That would require a skeleton, a prospect that would make a demon queasy. Instead, demons are magical entities, composed of essence and energies. On death, they disperse, leaving behind an ashy composite.

Don't be mistaken in thinking that it's similar to the ash left after a fire. Dab your tongue in Vile Ash and you'll soon understand where the "vile" comes from.