One of my mice has a small pink dot on her chest that looks a bit like a nipple, only I'm not sure it is because you can't see any others like this. I'm sure I would have noticed it before!
Could it be something bad, like a tumour?
Maybe some kind of problem with her nipple?
I tried to get a photo of her climbing the bars but it was so difficult. The cage bars are narrow and she kept on climbing. She's very shy so I'd prefer not to flip her over.
Sorry for the quality of the photo, it's all I can get right now.