I'm thinking of putting together a toastmaster speech about simple things we take for granted, that science doesn't actually have a clue as to how/why it works. I don't want to talk about complicated particle physics at the brink of our studies, but rather, really simple every day things, like "yawning"... Science has no clue as to why we yawn. And I think that's kind of cool.

What are your favourites? (these have to be observable, everyday things, not things that can be explained away like OBE, etc.)