A few weeks ago I got female two rats, Zip and Butter. Zip was apparently sick and died before we could notice. So I went back and got Whip, this time checking her eyes and all that stuff to make sure she was healthy. So I introduced them and they seem to get along fine. They sleep in the same box and everything. But every once and awhile Whip will run up and tackle Butter and they'll chase each other around, I haven't seen any serious wounds yet. But are they fighting or just rough housing like dogs?