They are dog like in behavior, and are actually domesticated just like dogs. They do not continually try to run away from you, as many other rodents will. Being social is one reason why you do want to have at least 2 rats, to keep one another company. They can become unhappy without a cage mate. Males raised together will not fight.
Rats are unfortunately very prone to respiratory diseases and tumors.
These for the most part can be treated successfully, if a veterinarian is consulted. See our rat FAQ's for more health information on the pet rat.