My Rat bit the rat it is used it so hard that it broke through the skin! ?

I just Noticed that Nibs ( the dominant rat) broke through Rilos neck. Anyways it is all dried up and everything, but Should I be worried if Nibs will kill him or something? He is always picking on rilo. I don't know if they are playing or not. Every time I hear Rilo screaming I go in and Nibs acts like he's not doing anything. He looks at me all innocent like.