Drop a cat from almost any height with its feet up and its back to the ground, and by the time it lands, it's facing the right way, feet first. Cats have been doing this in front of confused humans for a very long time. Working out how they actually do it turned into a real scientific puzzle, one that even briefly pulled in the same physics that governs a spinning ice skater.

A trick with a name

The behavior is called the cat righting reflex. According to Wikipedia's summary of the veterinary literature, kittens start to show it around three to four weeks old and have it fully working by six to nine weeks. A cat needs a bit of room to pull it off. Enough height and about two and a half feet of falling room, per the same summary, is what the reflex needs to fully complete before landing.

The puzzle that bothered physicists

Here's what made this genuinely hard to explain. Physics has a rule called conservation of angular momentum: an object that isn't rotating when it's dropped shouldn't be able to start rotating on its own once it's in the air, with nothing to push off. A falling cat has nothing to push off. And yet it flips over anyway.

The riddle goes back further than you'd expect. Live Science and BBC Science Focus both note that a French scientist named Antoine Parent wrote about the problem as early as 1700, while Isaac Newton was still alive. Nobody actually solved it for nearly 200 years.

The photographs that cracked it

The breakthrough came from a Frenchman named Etienne Jules Marey, a physiologist who invented a technique called chronophotography, taking a fast burst of images onto a single photographic plate, essentially an early form of film. In 1894, Marey used it to capture a falling cat at 12 frames a second and published the results in the French science journal Comptes Rendus, with a summary appearing in Nature the same year, according to the Public Domain Review.

The photos showed something nobody had actually seen with the naked eye: the cat starts completely still, with zero rotation, exactly as physics demands. Then, without ever pushing off anything, it twists the front half of its body one way while the back half counter rotates the other way, and finishes the fall the right way up.

How the trick actually works

Modern anatomy explains the "how" that Marey's photos couldn't. Live Science and the BBC both point to two features. Cats have around 30 unusually flexible vertebrae and no functional collarbone, which lets the front and back halves of the spine rotate almost independently of each other. And the inner ear carries small organs called otoliths, which sense the cat's orientation relative to the ground the instant it starts to fall, well before it's used any sense of sight to reorient.

The sequence is roughly: front half twists to face the ground, back legs and tail help slow the spin of the half that's already turned, back half catches up, legs extend to absorb the landing. All of it happens in a fraction of a second, faster than a person could consciously plan a single one of those steps.

It isn't a guarantee

The reflex is remarkably reliable, but it isn't magic and it isn't risk free. Live Science notes that cats falling from higher up, seven stories or more, more often land on their feet than cats falling from a shorter height, likely because the extra time in the air lets them fully complete the twist and relax before impact. But those same high falls also tend to cause more severe injuries when the cat does land badly. A cat with plenty of falling room and a working reflex is not the same thing as a cat who is safe on a ledge.

General information about cat physiology, not advice about pet safety around heights. If your cat spends time on balconies or high windows, secure screens are still worth having regardless of how good the righting reflex is.

Sources: Cat righting reflex, Wikipedia; How do cats land on their feet?, Live Science; The enduring puzzle of why cats always land on their feet, BBC Science Focus; Photographs of a Falling Cat (1894), The Public Domain Review. Photograph by Annashoots on Pexels.