Blood?

[Oxylepy]

The mice that I keep for my BP tend to do the "dominate" thing and beat each other up. Therefore I see blood splatter all the time on the glass from it. Sometimes they even ripe patches of hair out of each other too. Crazy rodents. Hope that helped.

This is an excellent point, they do tend to do this. Which is quite insane when you see huge chunks missing from their fur and fresh scabs :/