Falling cats seem to twist the front half of their body first
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When falling cats turn the right way up before they hit the ground, they have a secret trick: an area of the spine that is exceptional at twisting.
“We compared the flexibility of the thoracic spine and the lumbar spine in cats, and we found that the thoracic spine is very flexible,” says Yasuo Higurashi of Yamaguchi University in Japan.
Cats always land on their feet. If you hold a cat upside down and release it, the animal will quickly twist in the air and land safely on its feet.
How cats achieve this has challenged researchers for over 100 years. Three main ideas have emerged.
One is the propeller tail: the cat swings its tail one way and causes its body to rotate the other way. “The tail seems to be the least important, because if it doesn’t have a tail it can still turn around,” says Greg Gbur of the University of North Carolina at Charlotte, author of Falling felines and basic physics.
Another idea, the bend-and-twist model, suggests that the cat will bend its body almost at a right angle, then turn the front half one way and the back half the other. This means that the front and rear legs come into the correct position at the same time.
Or the cat could rotate front first and then back in a tuck-and-swing. To do this, it would extend its back legs while keeping its front legs cocked up, twisting its front half. Then it switched so the front legs extended and the back legs contracted, twisting the back half. This will mean that one pair of legs is correctly oriented before the other.
To find out what cats actually do, Higurashi and his colleagues conducted two experiments. In the first, they examined the spines of five deceased cats and twisted them to see how much each region could rotate without breaking. They focused on the thoracic spine, from the middle of the back, and the lumbar spine, from the lower back. It turned out that the thoracic spine had a range of motion that was three times greater than the lumbar spine.
Second, the team took high-speed video of two adult cats being dropped from a height of 1 meter. In both cases, the cats completed rotating the front tens of milliseconds before the back.
“My general impression has been that bend-and-twist is the most important thing, but this article actually makes me reconsider a little bit and put a little more faith in tuck-and-turn,” says Gbur. The highly flexible thoracic spine suggests to him that the front of the cat’s body can rotate more. Furthermore, in the live experiments, “it really looks like the upper (front) part of the body is correctly oriented first”.
Gbur emphasizes that the models are not mutually exclusive. “Physicists in particular love to look for simple models of how things work, whereas nature tends to look for the most efficient method, which may not be simple,” he says. “Cats are complicated creatures that make complicated movements.”
The study also threw up a curious detail. Both live cats rotated to the right when falling: one did so every time, the other in six of eight trials. Gbur says an audience member at one of his talks noticed that the cats in his videos also appeared to be turning to the right. “It looks like, anecdotally at least, cats seem to have a rough preference for which way they turn,” he says. It is not clear why; it may be that asymmetries in the placement of cats’ internal organs mean that it is easier to turn one way than the other.
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