If the snake does not eat remove the rat within 10 to 15 min PERIOD.
Now the feeding issue will depends on a few factor
A/ Is the husbandry optimum? That means we need a full description of temps, type of thermometer used etc
B/ Size and sex (confirmed) of the animal in weight because 4 feet means nothing to most people, as it can be 4 feet underfed or 4 feet over fed. It's will also help establish a few other thing that can be encountered with animals at a certain weight of animal of a certain gender such as sexual maturity, or if the animal is going through "the wall."
C/ Prey size offered and feeding frequency. Adults can fast to catch up if overfed so getting an idea on that is important, feeding should also be different if you have a male or a female.
Without more info it's hard to comment on why the animal is not eating at this point.