It happens you can either persevere and be patient, of course this should only be done with animals that have a good body weight because they need to be able to handle weeks even months without food.

Some snakes have nothing to do with rats I have an 06 male that will not touch a rat no matter what trick you use.

I have a female that used to be the same, even after long fast (9 months) she would still not touch a rat until very recently now she cannot have enough of them. (Took 4 years to switch that girl )