Science isn't entirely sure why humans and other animals yawn, let alone why yawning can be contagious -- but we've got some good hypotheses. Learn about them, from cooling the brain to spreading alertness, in today's episode of BrainStuff, based on these articles: https://science.howstuffworks.com/life/inside-the-mind/human-brain/question572.htm; https://science.howstuffworks.com/life/inside-the-mind/human-brain/contagious-yawn.htm

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