That can be a sign of boredom, just a stereotypical behavior. Make sure that they are getting out, getting their exercises, that they're stimulated enough, and they have enough enrichment. You want to be careful if they're biting their cage because, many times, cages are metal, and they can chip their teeth, so eliminate that as much as possible. Find toys or something else to distract them. You can hide their pellets around their enclosure, so they have to hunt for them.

Sometimes they grind their teeth when they're uncomfortable. It can be a sign of pain or discomfort. But sometimes they can do it when they're happy too. If you're scratching their chin and they grind it, they can do more like a teeth chattering thing- a tooth purr. It sounds like they're purring, but really it's their teeth. Otherwise, when they grind their teeth, they can be uncomfortable too. So it depends on the context of what's happening and if it's normal for them to purr.

They can see colors, which is one of their unique features compared to the rest of the rodent family. They can see at night, but not super well. So it's not like our night vision, but they can see a little bit at night.

They're eating all the time. They should eat hay throughout the day, and their GI systems are always working. They have to be pooping all the time because their intestines have to be going in order for them to absorb the nutrients. So constant eating, constant pooping, and constant moving are the way that their GI systems work and the way that it keeps them healthy. What goes in has to come out.

They don't. I guess sometimes their eyes can be a little bit open, but generally, they sleep with their eyes closed.