Why we yawn is not completely understood. But it is generally agreed that is an involuntary respira...
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Why we yawn is not completely understood. But it is generally agreed that is an involuntary respiratory reflex. This means that without deciding to do so, you open your mouth and your tongue moves back so you can take in as much air as possible. Then you take a long, deep breath. Your diaphragm moves down as your lungs begin to fill with air. Muscles between the ribs pull them up and out, which creates a larger space in the chest cavity. The lungs are filled to capacity, and then you slowly exhale, blowing some of the air back out.
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