If you have a pet rat, you may notice at various times the rat is exhibiting a behavior which is analogous to teeth grinding. The correct term for this is "bruxism."
And basically, what people who own rats call it "bruxing," and they'll say that the rat is exhibiting the behavior of bruxing.
What this means is it is a behavior where they are actually kind of grinding their teeth together, but it's thought to be associated not with teeth or dental problems, but is just a normal behavior that most people liken almost to the purring of a cat.
People think that when rats brux, they're content, they're happy, they're exhibiting that behavior because they're relaxed. People often find that rats will brux when they are spending quality time with them, when they are cuddling with them, when they are holding them and scratching them. And they'll exhibit a little bit of the bruxing-type behavior.
In most cases, it's normal. It's not considered to be cause for alarm. And it usually does not indicate that there is a dental problem unless it's excessive or unless the rat is showing symptoms of not eating or having other problems, where bruxing-type behavior may be a clinical sign.
But what most people recognize in their pet rats, is a simple form of bruxing, of grinding their teeth, making a little bit of a sound. And it's generally thought to be a sign of contentedness, and most people think of it as a positive sign.