My first and only thought so far is that it had to have something to do with the mice, meaning they either had some sort of parasite or infection that was not killed by Maurice's digestion process...although they didn't really look very digested. Also, he's a bit of a slow eater, so if the mouse was still alive I think we'd have noticed, but maybe not.
Either way, thank you ALL for your kind words and support, I really appreciate.