u/Feisty-Employment598

Hi! I'm here with a pet rat. I hope someone here has experience of having them. In February we bought the first rat, she's 8 months old. A month later we got her a friend, the same age and gender (both girls). For 2 weeks they've been separate, we cured the new one from flees. Their meetings were on a neutral territory, they were just interested in each other. After some time we've started letting them out to have a walk together. That's when it all started. The new one (Nora) started attacking the old one (Luna). Luna does absolutely nothing, she freezes and lets Nora climb on top of her. But! As soon as she climbs on top, she starts aggressively biting her. There were 2 bloody bites on Luna. Now every time they're out for a walk, Nora rushes to Luna to do the same thing, to bite her to blood. I'm scared she's gonna kill her. What do I do? Why is she so aggressive? The territory is neutral, they have separate cages, both get love and attention, we carefully introduced them to each other.