Originally posted by kingrattus
& mice, rats, & hamsters tend to nip, which is bad for a classroom. But I hardly ever hear of people of being bitten by guinea pigs.
Most mice never bite.

Mice would be a nice idea because they don't bite and they are easy to take care of. Fairly inexpensive, too. A downside is that they don't often return to their cage if they get "lost" so they would have to be VERY closely supervised.