What do you yawn? If one person yawns, the others also start yawning. Why?

Answer:
No one really knows for sure why yawning is contagious, or even why we yawn, but some studies have been done on this phenomenon. One popular explanation is that yawning allows you to get rid of too much carbon dioxide in your system and increase your oxygen supply, but this has been disproven. You can read more at these links.
http://www.howstuffworks.com/question572...

http://www.world-science.net/exclusives/...

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