What is the body trying to accomplish? How are they caused? What is actually happening? And why are they “contagious”?
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So we aren’t entirely sure why we yawn, but there are a few theories. One leading theory is that it is a mechanism to increase oxygen supply to the brain. When we are tired, our bodies slow our heart rate and therefore decrease oxygen delivery. The deep breath that occurs with a yawn allows for an increase in blood oxygen and therefore oxygen delivery to the brain while also expelling a large volume of carbon dioxide, effectively increasing brain blood O2 levels.
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