Professional herpetologists and pet owners have long debated the value of feeding live prey to reptiles. With some it's a good idea, with others it's not - in fact it can be dangerous.
One reason to avoid live foods is the danger of injury to your pet. When a live rodent is suddenly put into a snake's cage, the snake may at first react defensively, giving the rodent a chance to attack it instead. Alternatively, if the rodent escapes being eaten right away, it could launch an attack on the snake later as the temperature cools overnight and the snake becomes less responsive.
Even such formidable predators as adult anacondas can be at risk if attacked. In the wild, many snakes bear scars and even broken ribs from encounters with would-be prey.
If you absolutely must resort to live rodents, use only "pink" (unweaned) animals. These are not yet old enough to bite.
There are exceptions: A ready eater like the African clawed frog seems always eager to eat both living and non-living food. Marine toads have been observed to feed on dog food and vegetation but such is not a recommended captive diet. Salamanders, like frogs, do best with live prey while newts and other aquatic species will readily consume non-living food.
Pet stores sell frozen pre-killed mice in various sizes. Ideally you should offer your pet a mouse that can be eaten whole in one feeding, rather than offering cut-up parts of a larger mouse. This will ensure that your pet consumes the entire animal - skin, bones, and internal organs - all of which contain vital nutrients for your pet's health. If you must cut the animal up, make certain that your pet consumes it all over several feedings.