Yawning is not just a sign of tiredness or boredom - it is the body's method of keeping our brain cool, scientists have found.

打呵欠不仅是疲劳或厌倦的信号——根据科学家的最新发现，它还是人体用来自动调节大脑温度的一种手段。

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The cool woods and the fertile fields charmed him at first, but after two days of country life his old boredom returned.

起初，他对荫凉的树林和肥沃的田野还觉得新鲜，但过了两天的乡村生活后，他又对什么都感到厌烦了。

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These are gadgets used by teenagers who bite their nails and adults who want something cool to divert themselves from the boredom of their jobs.

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