I yawn, you yawn, we all yawn!! Everyone knows that... but who knows why?

BTW: it is just a random question that popped into my head. So I'm just asking out of curiosity!! :) :p

Yawning cools the brain.

Because the brain burns up to a third of our daily caloric intake, it generates a bit of heat. And our brains work better when they're not too toasty.

To help keep the temperature down, blood vessels in the nasal cavity and face send cool blood to the brain. The thought is that breathing through the mouth doesn't allow the brain to be as efficiently cooled. When you yawn, it causes the expansion and contraction of the maxillary sinus, a cavity located in the cheek. The sinus shoots air upward, kicking cool air at our headspace. Why We Yawn And Why Yawning Is So Contagious