The white stuff is urates, very normal! Now the fact that the bm looks like a mouse is not normal. It sounds like maybe a trip to the vet may be in order. Runny stool could be an indication of parasites, and if you can make out a mouse then you may have a regurg on your hands. I can't be positive on that, but I would recommend a trip to a good herp vet and get a fecal and general checkover!