This question from the project "My Planet" is answered by Maria Erofeeva, Ph.D., Senior Researcher, Laboratory of Behavior and Behavioral Ecology of Mammals, IEE RAS.
Where the saying that a cat has nine lives, and not seven or, for example, ten, came from, is not known for certain. This is probably due to the fact that the number 9 has often appeared in myths, legends and has long been considered magical, since it closes the cycle 1-9. Perhaps the agility of this predator and the ability to land on four legs led to the fact that people began to attribute magical abilities to it. However, in reality the cat only has one life.
It's just that nature has endowed the animal with a good sense of balance. Thanks to the developed vestibular apparatus, cats are not afraid of heights and can deftly walk on cornices, roofs and other heights. If they are to fall, they turn over in the air with their back up, spread their paws wide to the sides and land on all fours. As a result of such a maneuver, the surface of the body increases and the fall slows down as the "parachute effect" is triggered.
The tail acts as a balancer in flight. But this does not mean that cats without a tail are doomed. Such animals have learned to use their hind legs to maintain momentum.
In addition to a sense of balance, a flexible spine helps cats roll over in the air and spread their legs wide. Some have put forward opinions that cats do not have collarbones and that is why they are less injured when landing on their paws. It is not true. Cats have collarbones, but they are attached only on one side, which makes animals more flexible. For example, dogs cannot spread their paws this wide.
The most important thing during the fall is to have enough time to complete your acrobatic stunt. Therefore, height is critical. Paradoxically, a cat that falls from the ninth floor may receive fewer injuries than the one that fell from the first. "My Planet" strongly encourages owners of pets living in apartment buildings to be attentive to pets and not to leave windows open, as well as to equip them with special nets.
There is a theory that the minimum height necessary for the trick is 30 cm. Cats, however, are capable of injuring themselves by jumping from chair to chair, as well as of deftly walking on a mesh roof at a height of 3 m upside down and landing successfully when falling. So nothing is universal.
On a documented occasion in 2019, a cat survived on Sinyavinskaya Street in Moscow, having fallen from the 18th floor. Moreover, x-rays showed no fractures and slight pulmonary edema. Later it turned out that the previous evening the hostess opened the window to ventilate the apartment, and since there was no special protective mesh on it, the cat fell out. He was lucky, but there are also opposite cases.
Firstly, dexterity is not inherent in all domestic cats. Secondly, when falling, the cat can be very frightened, and in a state of shock, its inherent sense of balance can fail it. Thirdly, having fallen, the cat can hide in the basement or under a bush and sit there in a state of shock, not responding to the calls of those who are looking for it. Contrary to popular belief about the ability of cats to regenerate and treat themselves, they die from injury and disease, same as every other animal. So please, take care of your pets.