I feed live, in their enclosure. Usually I remove all of the cage furnishings, including the bowl, and just leave the snake and the rat. With enough experience, you can ready the snake's "body language" and tell whether or not they are interested in food. If a few minutes go by and I haven't seen the start of a feeding response, I remove the prey item. Leaving the rodent in the cage longer than that just stresses the snake out more and more.