A reptile’s willingness to feed in captivity is in part an indication of its acceptance of the circumstances of its confinement. Before you can expect your reptile to feed, it must become familiar with and feel secure in the environment that is provided. To ensure this occurs you must take into account the sorts of caging and husbandry conditions present. A settling in period of up to two weeks may be needed by some hatchlings, possibly longer for adult snakes. Always maintain a detailed feeding record of your reptile so that you can be sure that each specimen is being fed adequately. A well kept record book will make it possible to identify any unfavourable trends in feeding behaviour. The information that should be recorded are feeding dates, what was offered, and what was accepted. Along with your feeding records, it's also a good idea to record any other significant events as they occur (e.g. dates of skin sloughing, dates and descriptions of any medical treatment, dates of observed mating etc.)
All snakes are predators and most kill and eat other vertebrate animals in the wild state. In the wild, the prey items of pythons are suffocated by constriction and then swallowed whole. They are able to manage rather sizeable meals due in part to the extreme elasticity of the entire digestive tract and the fact that the skull and lower jaws are modified for the task. As snakes eat whole animals, they are able to obtain any necessary vitamins and minerals. They should not require any sort of vitamin supplementation in captivity if fed the appropriate types of food, though it is possible that they may benefit from exposure to ultraviolet light. From a nutritional standpoint, it probably makes little difference what sort of vertebrate animals are eaten, however, most species are fairly specific about what they will accept.
You can expect new born reptiles to be reluctant to feed for the first few weeks and often do not feed for a few weeks after birth, their food needs being supplied by residual yolk. Until a reptile has 'settled in', it should have its own cage, and of course be disturbed as little as possible. Over-handling is the most common cause of feeding problems that over-enthusiastic beginners experience. A good 'hands-off' policy is recommended for all reptiles until the fourth successful feeding in a row has taken place. If a new hatchling is subjected to excessive handling, provided with unsuitable hiding facilities, or subjected to conditions that are too cold or warm, you could be waiting indefinitely for it to commence feeding. A logical question to ask yourself when assessing the new arrival's cage facility is: Have I provided as closely as possible and practical, a captive scenario which reflects the natural environment of the reptile, particularly in relation to climate and substrate choice? Make sure that the reptile has found and is using the hide box or other retreat provided, and that the temperature within the retreat is appropriate.
A second step to take in your attempt to determine the cause of the new arrival's lack of appetite is to review the way in which the food has been offered. In the case of snakes, you should not feed until the snake settles into a hide box or similar retreat. Then place a dead prey item in the entrance for a couple of hours. If practical, you might cover the cage with a cloth sheet to avoid distracting the snake with your activities. If the prey item is not eaten, try a live one presented in the same manner. You can put a frog or lizard in the hide box with the snake, but when feeding rodents, leave the live prey outside the retreat. Do not leave a live adult rodent unattended with any snake. Lizards can be offered their food item on the end of a long pair of forceps. You can also try pressing the food item right up against the lizard's snout.
Every potential prey species has its own unique odour. You may find that a young snake that steadfastly refuses to take a 'pink' mouse will eat a pink rat, or perhaps a mouse with just a bit more size –and hopefully a more enticing scent or appearance. If you are finding that a frog-eating species, such as a swamp snake is refusing the frogs you offer it, try a different type of frog - or if allowed in your state or territory, perhaps a designated species of `feed lizard'. Just because an insectivorous lizard refuses to take one type of insect doesn't necessarily mean it won't relish another - don't give up until you've tried grasshoppers, crickets, cockroaches, and moths. When all else fails, mix an uncooked egg in a shallow dish and put the lizard's snout in the egg. It's surprising how many different species relish this treat.