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 real surprise: scientists still aren't completely sure why. So what is a yawn for?
Your guess
What do you reckon a yawn is actually for? (Clue: the famous “it's for oxygen” answer turns out to be wrong.)
Make a guess to unlock the hints and the answer.