Rats have a bad reputation. Most people freak out at the sight of them, without even giving the rat a chance to show he's not really that bad. For centuries, rats have taken the blame for the Black Plague, even though historians now say that it's not their fault. Rats make cool pets and serve an important place in the animal kingdom, so there's really no reason to hate them.
That being said, even a rat apologist like myself has to admit that the one place you definitely don't want to see one is inside your toilet. This disturbing scenario is actually something that has been known to happen in urban places around the world. Rats can survive in sewers, and if they happen to crawl through a few of the wrong pipes, they might be making an appearance in a very uncomfortable place. Recently, a team from National Geographic wanted to see exactly how rats can make their way from sewers to the inside of a toilet bowl.
To do this, they cut a toilet in half so the inner pipes could be viewed. They then placed the rat inside to see how it could swim up. The rat contorted itself around the pipes and found a small pocket of air to breathe in. Then, it continued onward until it popped up inside the toilet, giving a nasty surprise to anyone who might have been using it.
The good news is the chances of a rat climbing up your toilet are extremely small, so there's no need to be paranoid - but an extra check might be a good idea.
H/T: National Geographic