Why do we yawn when we’re tired?
In: Biology
we don’t know for sure, but there’s ideas. Yawning wakes you up a little, and people sometimes yawn before strenuous activity, which makes people think it’s your body keeping you alert. This helps to explain why yawning can be “contagious”; it’s a way for groups to keep each other more alert. But, there’s other ideas too, and if you want to read explanations that are much older than ELI5 check out the wikipedia page on “yawn”.
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