Rats are *awesome* pets. My sister has a pair of females. They're friendly, super curious, and surprisingly smart. She litter box trained them in approx 3 days. She lets them roam around her room in the evening.. they will actually retreat to their cage to do their bathroom business. They even tease the small dog by chasing her around on the bed. (We don't let the rats and snake play together)
Not only has she trained them to use a litter box, she has managed to teach them to do tricks using treats as rewards. Here's one of her super short videos... Its adorable, enjoy
YouTube - Rat Dance