I have had several snakes that will pounce on anything that was dropped in their cage and kill it within seconds. However, with picky eaters, this is often not the case. Many times, snakes decide that they don't want to eat, and for someone who is used to snakes with voracious appetites this can be scary or frustrating. While many people may panic that their snake is sick, that is often not the case. Many factors can keep animals from eating. Before you take them to a vet, you may want to try some tricks to help encourage them to eat their meals.
The most important factor is whether or not your snake is comfortable. A snake will often not eat if it is in an inappropriate environment. This can be due to various factors, but is usually from the cage being the wrong temperature or the wrong humidity level. Snakes also need to have a temperature gradient in their cage (different temperatures on either side of their enclosure). You should research your snake's specific preferences and set up your enclosure to mimic that. If your snake is comfy and happy, he or she is much more likely to eat.
Another reason some snakes won't eat is because they feel too stressed. This may also make them regurgitate food they've already eaten. One way to help with this is to provide a dark, quiet hiding space to make them feel safe and secure. You could even cover the whole tank if they seem very uncomfortable in it. That way, the next time food comes around, they may be in a better mood and more likely to eat.
Sometimes, snakes will simply want a different meal than you provide them. A snake may not eat if the meal you're offering isn't its favorite meal. It may be inconvenient or expensive for you to provide what they want every time, but you can make them think they're getting what they want by scenting the food with something else. For example, dipping a rat in chicken broth may make it more appealing to a tree snake which would be more likely to eat birds in the wild.
In the wild, some reptiles are cued to eat. This means, when something happens, they know it's eating time. Many species eat after a rain, so you can just spray them down with water before you feed them. You should research the animal you have and find out if it has natural cues that make it want to eat.
Another reason a snake might not eat is if the food isn't the right size. I always tell people that a snake is unlikely to bite you unless it feels threatened because it knows you are way too big to eat. A snake's food should be no larger than its widest section. Even if a snake does eat food that is too large, it can cause them to regurgitate or be sick. Remember, particularly with constrictors, that food can be too small. A full grown Burmese python can't eat a little rat. Not only is it not enough food to be worth killing, it also is too small to properly kill without risking being bitten or scratched.
I always advocate not feeding live prey, and one good reason is that animals may not eat it. Yes, an animal is less likely to eat frozen prey if it is used to hunting and killing; however, a reptile may be afraid to eat live prey, particularly if it has been injured in the past. If your pet seems to avoid the prey, try using pre-killed food and only moving it around a little (if at all) so your snake is less afraid.
These are just a few tips; however, if your snake skips several feedings, you should take it to a vet and make sure it isn't sick (or sooner if it is showing other signs of illness).