While I'm on things I actually learned in school: you know that thing about how in the Northern hemisphere, the water in your toilet is supposed to spin one direction, and in the Southern hemisphere, it's supposed to spin the other? It's a crock of BS! Nothing but an urban legend. The common pseudo-science explanation is that it's caused by the Coriolis force- a result of the Earth's spinning. Well, I learned in fluid mechanics class that the Coriolis force is absolutely tiny- basically everything overcomes it. The swirling you see when fluids drain is due to residual motion of the fluid that hasn't dissipated. To see the Coriolis force even begin to affect anything, you'd need a perfectly still body of water (roughly the size of a swimming pool) draining at a fairly piddly rate, and after a couple hours, you might see the beginnings of a Coriolis-induced vortex. So yea, in conclusion, the water in a toilet or bathtub spins a certain way when it drains cuz of something you did. And that reminds me:

"If a kid asks where rain comes from, I think a cute thing to tell him is 'God is crying.' And if he asks why God is crying, another cute thing to tell him is 'Probably because of something you did.'"
~Jack Handey