I'm sure this topic is brought up rather regularly in the rodents section, but I'm unsure of how to respond to this behavior. I apologize for the length of this post. We have 3 female rats currently. Our oldest, lucy, is about a year old and the more dominant of the three. None of the rats bother her and vice versa. A few months after getting her, we bought our second, ethel. The two fought occasionally in the beginning to establish a pecking order, but never anything serious. Anyway a few months later we introduced a third rat, fran. She was slightly smaller than the other two and picked on by ethel. But over all the three get along fine and have been nothing but angels. We've had fran in the group for about 3 months now, and both her and ethel occasionally wrestle, but no injuries are ever visible. Tonight, though, I heard a nasty screech next to me and they broke up immediately when I called their names. I checked them over and ethel had a small bite mark directly behind her ear that was bleeding a little. We separated the rats (keeping lucy and ethel together since they've been together the longest). I guess my question is... "should this separation be permanent?" Is it just a fight that escalated too far? Im actually watching the three try to get to eachother through the bars right now, and they've been fine before. It'd be unfair to isolate fran permanently from the others, since this has been a one time incident. Should I worry about coming down stairs and finding one dead if I reintroduce them? I'd appreciate any helpful input on this... thank you.