Yellow sore

Question
I have a mouse that I just got two days ago and it now has a yellow sore on its back and I do not know how he got it. He is with another male, but I haven't seen them fight yet...

Answer
The sore may be a bite, just because you haven't seen them fight doesn't mean they aren't having the odd scrap. Make sure the cage is big enough and they have plenty of places to hide. If they were brought up together they are less likely to fight.

If there is any discharge or if you are worried you could take him to the vet or ask the pet store you bought him from if they have experienced any similar problems (particularly from previous cage mates).

It may just heal up by itself. Please feel free to ask any more questions.