我们都知道打哈欠不仅仅是我们人类所有的，很多动物也会打哈欠，那么我们为什么会打哈欠呢？

我们先来学习一下打哈欠英语怎么说？Yawning就是打哈欠

下面和方向标一起来了解一下为什么会打哈欠

The act of yawning is baffling to experts for two reasons. One, it doesn't actually seem to serve any purpose. Seriously, when you feel a yawn coming on, suppress it. What happens? Do you go into convulsions? Is your face racked by pain? Does blood shoot from your nose? No. Not a damned thing happens.

Equally baffling, though, is the contagious nature of it. Yawn, and whoever sees you will yawn. When a chimpanzee yawns, the other chimps yawn. If you yawn, you can make a dog yawn. Seriously, try it.

Odds are you've yawned once just because you read the word "yawn" several times above. Why?

Science's Wild-Ass Guess:

Your science textbook in elementary school may have said that low oxygen levels in the blood triggered yawning, with the yawn providing a quick influx of the gas. That was the prevailing theory going back to the days of ancient Greece. As is usually the case though, it turns out people from back in the day didn't know what the hell they were talking about. In fact it's been found yawning may actually decrease oxygen intake. Makes sense, when you do hard exercise you don't start frantically yawning. You don't see athletes yawning in the middle of a sprint.

Unfortunately, the alternatives are quite a bit more insane.

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