Do cats really have 9 lives in real life
No they don't. I don't know where and when this presumption is made, but at least I can explain one thing that is related to it. Cats have something called "Righting reflex," that is the ability to correct their body orientations when it isn't in its normal position. The mechanism is amazing, first cats retract their front paws closer to the body, by doing this, they reduce their moment of inertia, and making the front body twist quickly. But, for the hind legs, the exact opposite happens. This reflex can help cats to land safely and preventing injuries. So this is the explanation why cats seem to have nine lives.
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Hope my answer helps you.