The Physics of Yawning

http://aplusphysics.com/community/index.php/blog/132/entry-1163-is-yawning-really-contagious/
http://www.theloop.ca/news/all/you-ask/article/-/a/3551768/Why-do-people-yawn-




Videos
https://www.youtube.com/watch?v=jGIbUK4nw00
http://www.nytimes.com/video/science/100000002525794/sciencetake-the-contagious-yawn.html