What Causes Us to Yawn?

Conventionally we think of yawning as a mechanism for getting oxygen to our brains when we're running low. However, research and testing shows that the brain is not found to be lacking in oxygen prior to a yawn. So if your brain is not responding to low levels of oxygen during a yawn, what is the reason for this odd but natural action? And why do yawns seem to be contagious?

The following video sheds some light on the most recent theories and evidence.

Try to contain your yawning while watching it!

http://www.youtube.com/watch?v=U8v9kopBaOs

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