Why Feed Killed?
The most common arguments presented for feeding live prey are that "feeding live is more natural for the animal - after all, no one kills their food in the wild" and "I like to give my animal a chance to hunt and kill because it really likes it."
The fact, however, is that captivity is not a natural state. Our reptiles and amphibians are not spending their days searching for food, hiding from predators, searching out favored microhabitats while avoiding aggressive members of their own species, hiding, vulnerable to predation and attack, during their shed periods. Instead they are housed (or should be!) in a comfy enclosure with all of their habitat needs met. If we wanted our animals to enjoy a natural state, we would never have acquired them.
As for needing the "thrill of the kill," that is anthropomorphism at its worst. What our reptiles and amphibians need is a large enough environment outfitted properly to give it enough mental and physical stimulation. For reptiles who are handleable, handling and that opportunity to be out of their enclosure provides the exercise and stimulation that they need, not chasing a rat or mouse around a small rectangular box.
Feeding killed or frozen prey is also safer for the reptile or amphibian. An animal who is not hungry will not eat. It will ignore whatever is going on around it. A prey animal left alone in a tank with a predator, however, is not so relaxed about the whole thing. Mice and chickens are usually terrified, spending their time cowering in a corner or trying to find a place to hide. Rats, however, come from bolder, and hungrier, stock. If left alone long enough with a disinterested predator, they will begin to eat whatever is around: your snake or lizard. Crickets and mealworms are similarly fearless and hungry. Rats have eaten their way into snakes, devouring the skin and flesh off their backs, exposing long stretches of backbone, even quite literally eviscerating them. Even crickets and mealworms will gnaw away at the skin and seek moisture from the eyes of healthy herps when left unattended in an enclosure without proper food and moisture for them. One of the most tragic things a vet or experienced herper sees is an otherwise healthy reptile or amphibian that has to be put down or is already dead from such prey feeding practices.
Live prey may also fight back during a feeding session causing severe injuries. Claws and teeth can bite through the mouth area, puncture eyes, cut through tongue sheaths, and puncture or slice through a coil of the predator's body.
There are those who will argue that it does not happen in the wild. There are also those who will argue that it does happen in the wild and that, being a natural occurrence, should not be avoided in captivity. It does happen in the wild. We don't see much evidence of it as the injured or crippled predator manages to hide away before dying or is itself preyed upon by another predator before dying or is scavenged after dying. I responded to a call where I found a wild gopher snake whose jaw had been fractured and half its tongue bitten off by prey who had successfully fought off a feeding attempt, its grossly swollen and bloodied tongue sheath dangling from the broken, crooked jaw.
Whether it happens or not, however, is immaterial. We are responsible for the health and well-being of our animals in captivity. That means keeping them properly housed, heated, humidified and fed. And that means keeping them safe from avoidable harm.
Defrosting Frozen Prey
First off, you don't feed out the prey while it is frozen! You do need to thaw it thoroughly and warm it slightly before feeding it out.
Freezing for 30 days kills off most parasites and other organisms that may be harmful to your herp. Prey may be kept safely frozen and fed out for up to six months after the date it was first frozen.
Remove the number of prey items you need from the bag of prey. You can place them in a clean plastic bag and soak in warm water, or leave in the refrigerator overnight to defrost, warming up in warm water. If you are skilled with your microwave, larger prey may be defrosted and gently heated using the defrost setting or lower power settings. Small pinkies can be quickly defrosted and warmed by holding under warm running water, or in a bag on top of a warm surface, such as the stove-top over the pilot light.
Always make sure that not only is the frozen prey thoroughly defrosted but that it is warmed up to a temperature above room temperature. You do not want your warm reptile eating cold prey, and warming the prey also makes it smell more strongly, and thus more attractive, to your reptile, and may be especially important when feeding reluctant feeders and when in the process of converting live feeders to killed.
Feeding Killed Prey
When first converting your herp from live to killed, try first offering a killed prey by dangling it from hemostats or kitchen tongs -- never hold the prey in your fingers! You may need to move it back and forth a bit to catch the herp's attention. Be prepared for the strike and quickly release the prey.
Converting Live Feeders to Eating Killed
If the herp is not interested, you might need to first feed a small stunned live prey, followed immediately by a freshly killed prey, then a prekilled prey. At the next feeding, start off with a freshly killed prey, followed immediately by a prekilled prey. When these are easily taken, go to offering the frozen prey.
Converting Non-Rodent Eaters to Rodent Prey
Some snakes available in the pet trade are amphibian and lizard eaters. This makes it not only difficult to obtain prey for them, but makes it rather difficult to convert them to eating rodent prey.
A suitable food such as a frog or lizard should be obtained and humanely euthanized for feeding. Instead of feeding it out, however, the lizard or frog should be rubbed all over a suitably sized prekilled mouse or rat to scent it. The scented rodent is then offered for feeding.
Another method is to pith (stick a pin or small nail) into the brain case of a killed rodent; this intensifies the scent and may attract a reluctant feeder into feeding.