Prolific Reproducers
Rats can reproduce as early as 5 weeks, and as long as they live. Please always keep separate the sexes or you will end up with babies. It's not a good idea to consider breeding unless you plan to improve the breed (ie. why create shorter lifespans or perpetuate tumors or lethal genes?), have kind homes lined up for all the babies (why send your beloved babies to uncertain fates), know how to recognize pre-/ post-/ birthing emergencies, how to keep mum from rejecting her babies, how to keep mum from injuring (perhaps fatally) dad, and special nutritional needs, for starters.
If you have both sexes housed under the same roof, be aware that the drive to reproduce will cause them to think up ingenious ways to escape, such as opening cage doors and chewing through wood and plastic. You will need to be extra vigilant that one sex doesn't get loose and end up near the cage of the other.
Territorial
Rats are extremely territorial. A pair or group of well bred adoptees will live together happily their whole lives. However introducing a stranger can wreak havoc within the colony. You cannot just put a rat into another rat's cage (aside from the quarantine issue) and expect them to be overjoyed. Unless the newcomer is introduced via a particular protocol, he or she may be killed or seriously injured. This involves introducing them at forst on neural territory, then.
Gnawers
Rats chew to keep their teeth down
