When I say this word, you will begin to feel very sleepy. In fact, yawning is so contagious that even the sight of the word "yawn" is enough to make six out 10 of us gape and bear our molars.
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Did contagious yawning help keep us alive?
Science notebook: When I say this word, you will begin to feel very sleepy. In fact, yawning is so contagious that even the sight of the word �yawn� is enough to make six out 10 of us gape and bear our molars.
