Why do We Yawn?
我们为什么打哈欠？

Do you yawn? There are about 20 reasons that scientists think are possible for yawning after research. They do not know exactly why yawning happens, but they do know many facts about yawning.
你打哈欠了吗？经过研究，科学家们认为打哈欠可能有20个原因。他们不知道打哈欠的确切原因，但他们知道很多关于打哈欠的事实。

We know that everyone yawns in the same way. First you open your mouth slowly. Your mouth stays open for about five seconds. You take in a lot of air and then push it out. Then you quickly close your mouth. We also know that yawning is contagious. When you see someone yawn, you yawn, too.
我们知道每个人打哈欠的方式都是一样的。首先你慢慢地张开嘴巴，张开大约5秒钟，吸入很多空气，然后把它呼出去，最后迅速闭上你的嘴。我们也知道打哈欠会传染。当你看到有人打哈欠时，你也会打哈欠。

Many people say they yawn because they are bored or tired. That might be true. People do often yawn before they sleep and after they wake up. However, we know that people also yawn when they are excited or nervous. Olympic runners, for example, often yawn before a race. Why is that? In 2007, scientists found that a yawn can help a warm brain cool down.
许多人说他们打哈欠是因为无聊或疲倦。这可能是真的。人们确实经常在睡觉前和醒来后打哈欠。然而，我们知道人们在兴奋或紧张时也会打哈欠。例如，奥运选手经常在比赛前打哈欠。为什么？2007年，科学家们发现打哈欠可以帮助温暖的大脑降温。

Some scientists believe that yawning makes you notice things more quickly. When you yawn, you breathe deeply. You also stretch the muscles in your face, mouth, and neck. Your eardrums stretch, too. Maybe this helps you to be quicker to notice things.
一些科学家认为打哈欠能让你更快地注意到事物。当你打哈欠时，你会深深地呼吸。还可以强化脸、嘴和脖子上的肌肉，耳膜也能得到强化。也许这有助于你更快地观察事物。

In some countries, people think yawning is not nice. People put their hands over their mouths to cover a yawn. In other countries, people think yawning is healthy. They think that opening the mouth very big can let good things in. When they breathe out, they think that bad things go out of the body with the air.
在一些国家，人们认为打哈欠是不好的。人们用手捂住嘴巴来掩饰打哈欠。在其他国家，人们认为打哈欠是健康的。他们认为张大嘴巴可以让好的东西进来。当他们呼气时，他们认为坏的东西会随着空气排出体外。

Scientists do not spend much time studying yawning. That is probably because yawning does not hurt. It is just something we do.
科学家们没有花太多时间研究打哈欠。这可能是因为打哈欠没有什么危害，只是我们做的事情。