Quote:
Originally posted by ozriceboy
It gives more oxygen when brain senses not enough.
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^ What he said!
When your brain is lacking o2, you begin to yawn. You yawn when you're tired because your breathing is slower (you don't exactly need to be breathing heavily in your sleep). As your breathing slows down to accomodate your rest, it also reduces the amount of air (and thus o2) that you are taking in. And now I'm leaving this thread because it's making me *yawn*.
