PLEASE HELP RAT IS HURT?

awww poor thing... Something like that sounds serious. When you say membrane and fat, yeah I'm worried. Have you tried covering the wound up? Bandaging it up, maybe? Other than that, I wouldn't treat it anymore than you have already. If you think about it, in the wild rats probably fight with each other all the time and their own wounds heal on their own. If he were in pain or if your rat sensed something wrong he'd do something about it or he'd show it. I'd say for right now, just sit tight there. good luck with your sweethearts. :)