  A thermally decoupled hidden sector of particles, with a mass gap,
generically enters a phase of cannibalism in the early Universe. The Standard
Model sector becomes exponentially colder than the hidden sector. We propose
the Cannibal Dark Matter framework, where dark matter resides in a
cannibalizing sector with a relic density set by 2-to-2 annihilations.
Observable signals of Cannibal Dark Matter include a boosted rate for indirect
detection, new relativistic degrees of freedom, and warm dark matter.
