Yawn

Yawning is a contagious, reflexive motion of opening one's mouth, inhaling air through the throat, and simultaneously stretching one's eardrums. There is no real answer to the purpose of the yawn; however, there are many theories including the brain needing more oxygen or a evolutionary behavior to warn others to stay alert during downtime. Many species of mammal yawn, and similarly find yawns from other members of that species infectious.