The undead are beings in mythology, legend, or fiction that are deceased but behave as if they were alive. A common example of an undead being is a corpse reanimated by supernatural forces, by the application of either the deceased's own life force or that of another being such as a demon. The undead may be incorporeal or corporeal. The undead are featured in the belief systems of most cultures, and appear in many works of fantasy and horror fiction. The term is also occasionally used for putative non-supernatural cases of re-animation, from early experiments like Robert E. Cornish's to future sciences such as chemical brain preservation and cryonics.