How do cats land on their feet?

The righting reflex works through a sequence that conserves angular momentum without needing anything to push against. The cat determines which way is up using the vestibular apparatus in the inner ear, then bends at the waist and tucks the front legs while extending the rear ones. Because a tucked segment rotates more easily than an extended one, twisting the front half one way and the back half the other produces net rotation of the front without an equal counter-rotation of the back. Reversing the tuck repeats the trick on the other half. The result is a full turn accomplished from a standing start in mid-air, which puzzled physicists in the nineteenth century until high-speed photography resolved it in the 1890s.

The reflex develops at around three to four weeks and is generally reliable by six or seven weeks. It requires height to complete, typically about a foot or more, which is why very short falls can leave a cat landing awkwardly. Cats also spread their legs after righting, increasing drag and slowing descent, and their skeletal flexibility and lack of a rigid collarbone help absorb impact.

The important correction is that landing feet-first is not the same as landing unharmed. Veterinarians treat a recognized pattern called high-rise syndrome, injuries from falls out of windows and off balconies, including fractured limbs, chest trauma, and broken jaws and palates from the head striking the ground after the feet. A frequently cited study found survival rates that were counterintuitively high for falls above about seven storeys, which has been interpreted as terminal velocity being reached and the cat relaxing into a spread posture, though the finding suffers from survivorship bias since cats that died on impact were less likely to be brought to a clinic. Either way, the practical conclusion is to screen windows and balconies rather than to trust the reflex.