I agree with Robin; the only time a mouse is actually going to damage a snake is if it's left in overnight to chew on the snake. If you supervise feedings there's no serious risk. Worst case scenario, the mouse gives the snake a little nibble and you remove it. No harm done. Or the snake grabs the mouse too far down and the mouse turns around and bites it for a few seconds. Snakes are tough; a tiny nip or scratch from a mouse (which is in and of itself uncommon) isn't going to cause a problem. This is what snakes are built to do; as long as you don't lock them up in a confined space with a mouse that they're not going to eat, they can take care of themselves.