Breathing

Do you ever think about those things you do that are entirely automatic? The 'keep alive' functions, like breathing. It's something your body has done, every moment you've been alive. And if it hadn't, you wouldn't. It's this incredible, ceaseless activity, which goes by unnoticed. Until you hold your breath underwater. Or in a 'who can hold their breath the longest competition'. Or to try and stop hiccups.
There's a small piece of graffiti in the uni biology department that says, 'you are now manually breathing'.