Why do cats always land on their feet?
Most cats can get their feet underneath them during a fall because of their unique skeleton structure and agility. Cats do not have a collarbone and the bones in their backbone have more flexibility than other animals. This makes bending and rotating their bodies easier during a short fall.
A fall of two or more floors, however, can seriously injure a cat. The impact of a fall from that distance or greater usually can't be sufficiently absorbed by the cat's feet and legs. This might cause the cat's head to hit the ground or serious internal injuries.
And keep in mind that any fall can hurt an animal. So make sure windows are properly screened and access to balconies and elevated porches is limited.
—The Fact Monster