Sweet Pea and Peter possible separation....

I think Peter is at that age where he is trying to assert his dominance or something. My gf and I went away for a long weekend and I left my sister to feed and water the rats.
I got home and Sweet Pea has a giant cut down her back. It's healing up well... But it's sore... 90% of the time her and Peter get along fine. For an hour the 2 of them were sleeping together in the hammock...
Everybody is spayed/neutered.
But that other 10% they are fighting... Usually no blood is drawn. He got her on the ear once... Just a small cut... But this is a really big cut down her back...
Im sure the rescue I got home from would take him back. I've only had him for about a month now. So he should be like 16 weeks I guess. And then this morning he bit the crap outta my gf. And he kept trying to get me... Which he's never done before....
So idk if he freaked out cuz we were gone for 5 days... Or what... Sweet Pea is like a year old...

I cleaned it with a little peroxide and got a picture.

Just a couple questions that might help narrow down the issue:
- Have they been having these fights since you got them or are they a more recent thing? I'm just wondering if there might be something in their environment (another animal maybe?) that is stressing him out.
- What kind of cage are they in?
- How was Peter acting when he bit your gf? Was he caught off guard or was it more aggressive?

You said he's neutered so hormones shouldn't be an issue. Where was he was he bite you and the gf? Was he in his cage? If so, he might be cage aggressive. How long did you do intros for? Other than that injury, did you check everyone over for scabs? Mites/lice can make them crabby.

Everyone is clean as a whistle other than that one scratch. Checked everyone over after I saw that.
Intros went way fast and I got some crap on here about it. About an hour in a tub together. And then 30 minutes in a carrier together. And then into the cage they went with me supervising like a hawk. Nothing unfriendly until into the cage. And then it was puffed up wrestling. But no one was ever bitten. They just pushed eachother around. But that wrestling has been going on since then... And like I said. 90% of the time everyone is cuddling and playing together. Well Buck is lazy so he doesn't play much.
And yes when Peter bit the gf it was cuz she stuck her fingers up to the cage. So I figured it was an over zealous food snatch attempt. Until I reached in to pet him and he started getting a little to nippy with my fingers. So I fussed at him but I kept trying to pet him and he kept standing up to get at my fingers. Finally I grabbed him with a towel and he was fine... I'm really hoping it was just stress from me being away for 5 days... I don't want to have to separate them...
I wasnt concerned about the dominance thing cuz no blood was being drawn... But now...

Cage is a DCN

I don't want to have to give him back to the rescue I got him from. But I can't have him hurting my other two. Please someone help me...

Did he BITE the two of you where blood was drawn, crime scene looking rat bite? Or just nip possibly harder than you'd like? That intro was rather quick and you might want to consider trying again. Just separate and start over. However, if that's the only injury so far it could look worse than it actually was. I've had them on my ratties too where they tussle and one zigs when it should of zagged and its a tear not an actual bite. Yes its a tooth, but they don't mean to do that. When you see the incidents happening and you have a definite aggressor or trouble maker you can try the time out cage. Put the rat in an empty travel cage for 10 minutes and leave them alone - no stimulation, don't talk to them, etc. Do this every time he/she misbehaves. Now, on the other hand, when they are good - don't nip, walk past each other or look like they are going to tussle, but walk away reward them with a small treat and praise.

He bit her and broke the skin. Drew a little blood. But not murder scene blood...
Thank you dspch911 you've made me feel a lot better! I've never had this issue before. And I wasn't sure how to handle it.

I would keep a close eye and if there continues to be issues with them getting along then I would second dspch911's suggestion of separating them and redoing intros at a much slower pace.

When was he neutered?
You could start intros all over again but this time go slower. The alone time when not being intoed might make him want his family back and be nicer. If it's only been a month since his neuter, I'd give him more time to adjust and just keep everything as it is.
Are you the main caregiver? If so, you being gone could have stressed him so much that he started to use his teeth when bullying.
And I do want to add that the slice, although big, is still not really an aggressive bite. That looks like he mounted her, went to power groom her and she decided she didn't want it so got sliced in the commotion.

Thank you jorats! That makes me feel much better.
Yea my gf and I are the only ones that interact with them. They're in our room. And both of us were gone. So I'm thinking it was the stress. They keep having dominance issues. But I think it's just Peter and his age. And yea I think he's only been neutered for a little over a month now. I have a DCN and have been debating shutting them into 1 level to hopefully prevent any sort of territorial behavior especially since there are only 3 of them... But I have the timeout cage out in case we need it.
The other day Buck refused to let Peter drink from one of the water bottles. And they both just stood there puffed up leaning against eachother...