十万个为什么·科学阅读30篇（5）
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Why Do We Yawn?
人为什么会打哈欠？
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Yawning happens when our brain needs more oxygen.打哈欠是大脑需要更多氧气的表现。
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It also helps cool down the brain a little bit.它还能略微降低大脑温度。
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We yawn more when we feel tired or bored.人在疲倦或无聊时更容易打哈欠。
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Even babies yawn before they are born.胎儿在出生前就会打哈欠。
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Yawning is contagious — seeing others yawn makes us yawn too.打哈欠具有传染性——看到别人打哈欠，自己也会跟着打。
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Scientists think this may help groups stay alert together.科学家认为这可能有助于群体保持同步警觉。
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Taking a deep breath during a yawn fills lungs fully.打哈欠时的深呼吸能让肺部充分充气。
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Then we feel more awake and ready to focus.随后我们会感觉更清醒、更专注。