The cat righting reflex is cat's innate ability to orient themselves as they fall so as to land on their feet, often uninjured. The righting reflex begins to appear at 3-4 weeks of age, and is perfected at 7 weeks. They are able to do this as they have an unusually flexible backbone and no collarbone. After determining up from down visually or using their vestibular apparatus (in the inner ear), they rotate their upper body to face downwards and their lower body follows. In addition to the righting reflex cats have a number of other features that will reduce damage from a fall. Being small, having a light bone structure, and thick fur decreases their terminal velocity. Furthermore, once righted they may also spread out their body to increase drag and slow the fall to some extent. A falling cat's terminal velocity is 60mph whereas a falling man in a free-fall position is 130mph. At terminal velocity they also relax as they fall which protects them to some extent on impact. Padded paws will also soften impact.
Using their righting reflex, cats can often land uninjured. This is, however, far from always the case, and cats can still break bones or die from falls. In a study (in the Journal of the American Veterinary Medical Association) of 132 cats that had fallen from buildings, it was found that cats were most likely to die if they had fallen about seven stories. Below that height they may not have reached terminal velocity and would hit the ground with less force. However, if falls were further than seven stories the chance of cats dying also decreased as they had more time to right themselves, spread to increase drag, and relax.