When ferts play it can be very vicious. Especially when they are breeding. We have 14 ferts right now. We had to get a pet shop license because we have so many. Usually when they have a grudge against one or another it may take time for the pay back. You have to let them duke it out or it will continue later. You have to montor he fight but they will play with each other again. We have 2 brothers from different litters, Sasquatch ( 6 toed polydactil) and Gator that would not get along. We tried Bitter Apple and everything else we could think of. Even washing the sent to make it the same. Finally we just had to let them duke it out. Now they are OK. They still duke it out once in a while. They sleep togeather but won't play yet. [Posted in FML issue 3269]