UPSIDE-DOWN SLEEPERS refers to two animals that sleep in an upside-down position: BATS and sloths. BATS are small, flying mammals that hang upside-down from branches or ceilings while they sleep. Sloths are slow-moving, tree-dwelling mammals that also sleep upside-down, usually hanging from a branch. Both animals have adapted to this unusual sleeping position, which helps them to remain safe from predators.