Mystery #4Tier 2-3brain / body
Why do you yawn?
You see someone yawn and, almost helplessly, you yawn too. It happens when you're tired, bored, even after exercise. Everyone does it, animals do it, and here's the surprise: scientists still aren't completely sure why. So what is a yawn for?
Your guess
What do you reckon a yawn is for? (Clue: the famous “it's for oxygen” answer turns out to be wrong.)
There's no single magic word to type, have a go in your own words, then reveal the answer to see how close you got.
Make a guess to unlock the hints and the answer.