This is a type of monster that is immune to starvation and dehydration, it may not even have to sleep or breathe. Much like the Energizer Bunny, it just keeps going and going and going. Perpetual Motion Monsters are either explicitly supernatural, a set super advanced Mecha-Mooks, or both. Compare Automaton Horses (not the mechanical variety), where this is noted as one of the features that make fictional horses unusual. Compare Forgot to Feed the Monster when this is averted. Related to The Insomniac type 4 (doesn't need to sleep). A Sub-Trope of The Needless. Examples: