Rats have teeth that grow continuously throughout their lives. This means that if you don't take care of your rat's teeth, they can get too long and cause problems. Long teeth can make it difficult for your rat to eat, and can also lead to infections.
The best way to keep your rat's teeth short is to give them things to chew on. Chew toys made specifically for rats are available at pet stores, or you can give them safe household items like cardboard tubes or untreated wood blocks. Encourage your rat to chew on these things regularly, and their teeth will stay nice and short.