Try blasting the head of the mouse with a hairdryer or (if you can stomach it) Brain the mouse (use a toothpick, poke a hole in the skull, wiggle the toothpick around, and put some of the juices on the nose of the mouse) . I wouldn't freak out too much BPs can go a pretty long time without eating and are known to be finicky/go into fasts, but definitely keep an eye on him, especially because he's so young