Some of them are just difficult. 5 of mine will eat rat or mouse, f/t or live, and any size they are physically capable of swallowing. Then there is the mojave. The rat must be of a particular size which is ridiculously undersized for her, and they must be live.
She will occasionally accept 2 small live mice in lieu of her undersized rat, but that is as far as she will move in the direction of being reasonable. I'd like to kick her butt, if I could find it.