In my eyes This is the world we have become accustomed to.. Meanness towards one another is not just human's.. It's in animals too.. I mean.. this question can go on and on for centuries.. Why are people mean to each other? Why is life not fair? Why do people fight? Why do some animals get along with others and some don't? In the meantime.. You have to understand.. Life is just full of reasons why meanness occurs.. A day not going right, waking up on the wrong side of the bed, jealousy, betrayal, hungry, mood swings, lack of energy, being bullied..Dominance... I mean You take into consideration all the reasons meanness occurs and you have over 1000 possibilites..The Same reasons human's are mean to each other is the same reason's animals are mean to each other.. They might get into arguements and fights and not agree with one another.. You don't know what's going on in their world.. Best to resolve the issue.. If the problem occurs frequent.. Maybe you can seperate them.. I know before my dog passed away when she went into heat the two boys would fight.. It would be nonstop.. But as soon as she got out of heat they would be fine again.. One time it got so bad that we had to get rid of one of the dogs.. They just would not fighting and we were afraid one of them would kill each other..... When she got out of heat it would have been fine again..But i couldn't risk not being home one day and the fighting starts and we wouldn't be there to seperate them.. but the level of anger that was in them both was a level i never seen before and decided we should end it there.. So Maybe You should watch your animals more closely and see just what could be the cause of the fighting Sometimes they answers may be right in your own grasp.. However i do hope that this issue has resolved itself out..