Rabbits are raised for meat, and fed hay and Rabbit Chow. The diet is standardized, and clean.
Cats eat whatever, and the rodents they scrounge may have been exposed to rat poison. Most backyard breeders of puppies whot are going to hand off the animals to any responder from a Craig's List ad are probably feeding the cheapest food they can get.
Who in their right mind, would want to put that into a snake?