"Sometimes, a rat's eyes may vibrate rapidly in and out of the eye socket, a phenomenon called eye boggling. This odd eyeball movement often occurs at the same time as bruxing, or tooth grinding. The reason bruxing and eye boggling occur together is anatomical: a part of the muscle that pulls up the rat's lower jaw passes through the eye socket, behind the eyeball. When a rat grinds its teeth, it moves its lower jaw rapidly up and down, and the contractions of the jaw muscle vibrate the eyeball in and out of the socket in time with the jaw.
Eye boggling is associated with intense bruxing. Anecdotally, eye boggling occurs at times of great contentment and relaxation."
Binro the Heretic Be prepared to clean their cage every day. They just piss and shit constantly as they walk around. It's the reason I only "sort of" miss Rat-rat. I'd dump the old litter and clean the inside of the glass every afternoon. By the following afternoon, the litter would reek and there would be a greasy urine film at rat height all the way around the cage.
Get a hamster instead. They're twice as adorable and will hold their poops & pees so they can deposit them in one corner of their cage. You can even train them to use a little hamster-sized litter box.