Snakes in the wild may eat mammals, birds, other reptiles, amphibians, fish, worms and insects. When considering purchasing a snake for a pet, make sure it is eating at the pet store prior to bringing it home. Small snakes that are eating pinkies usually graduate to consuming older and larger mice as they grow. You may have seen advertisements for pinkies, fuzzies, hoppers, weanes or weans, smalls and adults. These are just different ages and sizes of mice destined to be used for snake food.
Rats also come in different sizes.
Since snakes consume their dinner whole, for the most part, they are usually getting a good balance of nutrients. An exception to this occurs when a snake is ill or for some other reason, will only consume pinkies. Pinkies are baby mice, and therefore don't yet have a well-developed skeletal system. The bones of a pinkie contain more cartilage and less calcium than the bones of older mice. If a snake eats pinkies as the sole or major portion of the diet, there is a chance that it might develop calcium deficiency after a period of time.