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When we get wet, we need a towel to get ourselves dry. When a dog gets wet, all it needs is to shake its body. A study in 2010 showed that a wet dog can throw off half the water on its body by shaking for less than a second. In fact, this common act of dogs works better than a washing machine. The study found that animal shaking begins with the head and ends with the tail. During a shake, the animal's head, body and skin all move. Smaller animals must shake faster than bigger animals to get water off. For example, in one second, a rat can shake 18 times, a dog 6 times, and a bear 4 times. Bigger animals can get their bodies dry with fewer shakes. For animals, shaking is not just about getting themselves dry. It is also about saving their lives. Being wet makes animals heavier, and that makes it harder to run. In the animal world, how fast an animal can run often decides whether it will live or not. Maybe that's why the “wet-dog shake” has become a common habit of many animals. skin 皮膚