{TED video} why yawning is contagious

Last week I was traveling back in Massachusetts. One night when Larry called, it was late here on the east coast and I was so sleepy that I couldn't stop yawning. I would yawn which made Larry yawn which then made me yawn. We could have collapsed into a warm, happy heap of sleepy at that point.

I've often wondered why when you yawn it makes someone else yawn. This morning I found the answer. Yes, you will yawn as you watch the explanation from TED-Ed. Enjoy.