You go on a big hike. That evening you feel fine. You wake up the next morning — still fine. Then on day two you try to sit down and your legs scream. Why did it wait?

You will spend somewhere around a third of your whole life asleep. That's an enormous amount of time to spend doing nothing — which is a good clue that you aren't doing nothing.

Try to tickle your own ribs. Nothing. Now get somebody else to do exactly the same thing and you'll be on the floor. Same fingers, same ribs — so what changed?

You hear yourself in a video and think: that is not what I sound like. Everyone else in the room thinks it sounds exactly like you. One of you is hearing something the other one isn't.

A fever feels like the illness winning. Here's the odd part: nothing is heating you up. You are doing it, on purpose, and your body is working hard to keep it there.

There is a hole in each of your eyes. Not a small flaw — a proper gap, with nothing in it at all. You have been looking through both of them your whole life and never once noticed.

Stay in the bath a while and your fingers go all crinkly, like raisins. Everyone will tell you your skin soaked up the water. Everyone is wrong about this one.