Simply put: snakes don't eat if they're not hungry. When they're hungry they go into what can best be described as "kill mode." They tense up, start to twitch, and will lunge at anything edible. When a snake is in kill mode, it will kill a mouse. If you've ever seen it happen, you know its not even a question. The mouse will die. Quickly.

But only if the snake is hungry.

Please, please, please, please don't feed your snake unless he's hungry. If he's not hungry, then he won't go after the mouse. However, the mouse will definitely freak out and fight the snake. Not 'fight back' against the snake, because the snake won't do anything. The snake, not being hungry, still won't try to kill the mouse. He'll just try to get away from it, which he can't do because he's in a terrarium. And that's how snakes get hurt.

Please be careful. If you can, buy frozen mice at the pet store and thaw them out before feeding them to your snake. If your snake refuses to eat pre-killed mice, feeding him live mice is okay. But don't do it unless he's hungry, and don't ever walk away from the cage until the mouse is clearly dead.

Its grizzly to watch, but its over after a minute or two. The discomfort of watching your snake feed on a live mouse is nothing compared to the pain your snake could wind up suffering if you aren't there to supervise and, if need be, intervene.