let the snake figure it out on its own, also dont hover and watch, sometimes that scares them off the food.

Is this your first feeding? snakes will kill or attempt to kill all there food, its in their nature not to eat anything until its dead, even if its prekilled they dont know that. They will hold on as long as it takes til they think its dead. something you should try is once your snake has taken the food and constricted it, pull on the tail slightly a couple times, this will mimick the mouse trying to escape and make the snake think its actually killing its prey.