Why you yawn sometimes?A yawn is extended gaping of mouth followed by more rapid closure. It is impossible to resist a yawn.
Why does it occur? Because of tiredness? Or sleepy?
What I know about yawning is
1) As far back 400 BC,Hypocrates thought yawning removed bad air from the lungs before a fever
2) In 17nth & 18th century, doctors believed yawning improved oxygen in blood
3) Recently, people believing that yawning cools down the brain.
The truth is that nobody knows the true biological function of a yawn.
Interesting thing is that yawning occurs in all species. It is contagious.
Watching someone yawn or reading this thread or some threads in this forum also can lead you to yawn. Why?
Dear members, what you know about yawning?