At dusk, a zebra's striped flank may scarcely shift, even as the animal dozes upright; beneath that apparent stillness, its limbs use a passive stay apparatus, a set of tendons, ligaments, and joint geometry that bears weight with little continuous muscle work. Stillness is not surrender. Rarely is this posture a sign of deep, uninterrupted rest: zebras can drift while standing, yet they usually l...More