Thank you for the advice. Again, this is my first time with rats. I don't mean to make mistakes with them, I just want them to be happy and healthy and know they have a mom and dad to love and trust.
All of the bites that drew blood were surprises. For example, when he drew blood this evening, he had climbed into my lap, found my fist, and didn't bother with the nipping - he attacked with a punching forward lunge. I am nervous about his reactions to hands, and I offered my hand to him for the sake of you and the others watching the video. After eating his treats, having rat talks with Castielle and marking out his area, each evening, he comes into my lap and looks for a hand to bite, and when I hold my hand up so he can't get to it, he stretches as high as he can after it, and has jumped up trying to bite. It's almost like he's LOOKING for a hand for the sole reason of biting it at this particular point.
Almost all of my interactions with Mimo since last Saturday, whether Castielle is there or not, start out with him being curious and gentle but not particularly friendly, and then end up with a surprise bite - a surprise, because maybe he had been grooming or sniffing before. He doesn't bite skin at all unless it's on fingers. And again, for almost a week, he seemed very quiet and gentle until he delivered an unexpected, violent bite, and kept on looking for hands and fingers to attack afterward.
Some comments/questions:
I should scoop him up while he is marking his area?
There is a lot more in the cage; I'd taken it out to refresh the liners just before the video, and finished with the cleanup afterward.
I'm not sure of their ages. Their original owners claimed when they took them to the SPCA that they had been together all of their lives. But they also claimed that Castielle (white) is the alpha and the aggressor, and that Mimo (black) is the subordinate. They were abandoned because they were "fighting" with each other.
I understand that there were no real fights during this video. It was a very nice playtime. The ones that end up with Castielle bleeding usually happen in the early morning hours with a great big squeal and a clatter, and we run into the room to find Castielle hiding somewhere and Mimo puffed up. I'm not sure at all what the actual fight looked like, just that Castielle has scabs on his rump and a bleeding tail.
The two bites that I showed on my index finger have been treated aggressively, but the fingernail is still cracked in half. Below are pictures of the one on the fingertip when it was fresh. The one that caused the bruise happened just afterward.