Rushed into rat room after hearing loud distress squeaking to discover that Sero got bit on the left side of his face. All the other males were laying about, looking at me innocently (go figure!) The skin surrounding the area appears to be bruised. Definitely going to have to keep an eye on this to make sure it doesn't become an abscess.  Speaking of which, while examining Sero, I noticed that Vaux, who was standing up with his front paws on the cage side, has a small pea sized lump on his abdomen. I suspect an abscess since he is male (likelihood of it being a mammary tumor is much more uncommon). Applied a warm compress.