I brought home two baby rats over a week ago, and they've been in their own cage next to my current rats' cage. The first introduction ended up in an emergency vet trip, and I've been scared to try another introduction. How old should the young rats be before I introduce them? I've been waiting until they get larger. The current rats puff up and huff at the babies whenever they're moving around. Is this normal? They're female rats and I really didn't expect them to be so aggressive.