Both mice were sweeties. We eventually lost both of them to tumors. I think they were fibrous skin type tumors - loose under the skin, not in any particular organ... but they eventually made it hard for the mice to walk around, and probably invaded other organs. The hardest part about keeping rodents for pets is that they almost always die a gradual death from cancer eventually, and unlike cats or dogs, it just doesn't make financial sense to have the tumors removed surgically (surgery is also dangerous on animals that size because the anesthesia is so tricky, etc). It's hard to be faced with the decision of euthanasia or suffering.. and even harder when the euthanasia costs $25, as it does at some veterinary clinics. If the rodents rae lucky, they'll pass away peacefully in their sleep, but if not, the decision at the end is always a difficult one, and given their lifespan, you end up making those decisions every two or three years, if you keep rodents. But, most people outlive their pets, and most people admit that the joy they brought to our lives is worth the loss we feel when they're gone. Blah, enough of that!