While in the wild most snakes will kill their prey to eat. Snakes also eat whatever they find, even if it's dead. So the idea that a pet snake needs to be fed live prey is a myth that needs to be dispelled.
Snakes will eat a variety of small animals and insects; some will even eat goldfish swimming around in a small bowl of water. Small snakes such as garter snakes can eat worms, insects and goldfish. Most of these animals and insects cannot harm a pet snake when placed into its cage.
Larger snakes require larger meals such as mice, hamsters, and rabbits. Some snake owners will use free kittens as snake food, or find free rats and use them as snake food. Putting a live mouse into a cage with a snake could be a lethal mistake for both of the animals. Mice, hamsters and rabbits will fight to live, inflicting bite after bite to the snake until they take their last breath.
There have been instances where snakes have been so badly bitten by their prey that they actually die from infection or a lethal bite to the head. Live prey can also have mites or fleas that can infect a snake.
When we speak of dead prey usually we mean frozen mice, hamsters and rabbits. These food animals are humanely killed and then frozen to use as food for snakes and other reptiles. Being in a freezer will kill off any mites, fleas or other pests that might have infested their fur and gotten onto a pet snake or in its cage if they had been fed alive.
This is also a more humane way for prey animals to die. It's not humane for an animal such as a baby hamster to live their last few moments in pure terror, being slowly suffocated to death when there are safer more humane ways to feed the pet snake.
To feed a snake dead prey, all that is required is to thaw the prey animal out either at room temperature or in a bag surrounded by warm water and then dropped into the pet snake's cage. The snake will know what to do with it.
Most snake owners think their snakes will not eat pre killed animals but they will and it's a more humane way to feed a pet snake.