Hi, I know this is difficult. Intros can be scary and potentially dangerous, but mostly terrifying to us humans. Puffing up is a very emotional expression; they can be communicating uncertainty, lack of confidence or fear. Don't mistake fear and defensiveness as aggression, because sometimes it's that simple...they are scared of the other rat and the situation and don't know what to do except make themselves bigger! Before you think about neutering the other rat, give them another chance or two.
Your boys need to start all over with intros, like they've never met. First, I would separate the cages so they can't see each other. It's like two dogs on either side of a fence...they become more territorial and aggressive if they can see each other but not interact. Put a blanket between them or move them to different rooms and give them a few days, then start swap bedding between their cages so they know their smells.
Intros can take days, so don't give up too early. Their situation has changed. They will decide who is the alpha now, and even when they are screaming bloody murder, if they aren't drawing blood or hurting each other, then you have to hunker down and let them sort it out. If they are in a neutral open area, have a dustpan ready to stick in between them if they really fighting, or a towel to throw over them. That can distract them and de-escalate an aggressive situation.
Your boys need to start all over with intros, like they've never met. First, I would separate the cages so they can't see each other. It's like two dogs on either side of a fence...they become more territorial and aggressive if they can see each other but not interact. Put a blanket between them or move them to different rooms and give them a few days, then start swap bedding between their cages so they know their smells.
Intros can take days, so don't give up too early. Their situation has changed. They will decide who is the alpha now, and even when they are screaming bloody murder, if they aren't drawing blood or hurting each other, then you have to hunker down and let them sort it out. If they are in a neutral open area, have a dustpan ready to stick in between them if they really fighting, or a towel to throw over them. That can distract them and de-escalate an aggressive situation.
