打哈欠为什么会传染？

You yawn, and your friend yawns too. 你一打哈欠，朋友也跟着打。 Why is yawning so catchy? 哈欠这东西，为啥这么会传染？ Scientists think it is your brain's mirror. 科学家认为，这是大脑在照镜子。 When you see a yawn, your brain copies it. 你看见别人打，大脑就偷偷模仿。 It shows you understand other people. 这说明呀，你能懂别人的感受。 Even dogs can catch a human's yawn. 连小狗，都能被人的哈欠传染。 So next time, yawn back and smile. 下回被传染，就笑着打回去吧。