Why people yawn when they are sleepy? Are there any biological reasons behind yawning?
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indeed. when brain feel tired, brain tells lungs to do biiiig gulp of cool air. sudden intake of air and stretching of the lungs and diaphragm increases blood flow and brings new oxygen into the body. this can help to do a little tiny jump start to attempt to make body less tired. it doesn’t really work but for some reason humans haven’t evolved past yawning yet…so it must serve some other purpose.
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