Snakes and lizards can throw up for several different reasons. The first thing that you want to check is your cage temperatures. If the animal does not have a good hot side or basking spot, it may not be able to get warm enough to digest properly. If the food rots faster than they can digest, they may throw it up. Stress after eating can also cause them to get rid of their meal, try to keep handling to a minimum after eating. Eating too much too fast, or eating a prey item that is too large can also cause this. If it continues to happen and it is none of these problems, bring your pet to a reptile vet and have them checked out.