The folks over at ASAP Science have pulled out their dry-erase markers to explain why we yawn. It's an appropriate topic given that today is World Sleep Day.
But, as these smart people explain, yawning isn't necessarily about being tired. Guinea pigs yawn to display anger. Human fetuses yawn. We likely yawn as a form of empathy -- which explains its contagiousness -- and we also do it to keep our brains from melting.
OK, that's an exaggeration. But many believe we yawn to pull extra oxygen into our lungs; ASAP says, rather, yawning likely helps to cool our brains when needed.
See how long you can make it through this video before you yawn. (I yawned before the title appeared.)
Wake up! And follow me at @AmyTheHub