Please, please do NOT leave the room with mouse in the enclosure with your snake!
In my experience, when they are fearless and start sitting on the back of the snake is when they get curious and start nibbling on the snake. Those nibbles turn into bites, which turn into ripping, tearring bites!
When our snakes are not in feed mode, it's like they are a gentle scared puppy who will not defend itself.
This is one big reason why many folks refuse to feed live in the first place.
Never leave them alone with a live feeder.
I learned the hard way as a noobie.
Best