Although a snake is a pretty formidable adversary for even the toughest rodent, a feeder can occasionally get lucky and manage to bite its predator. Most feeding bites are much less serious and pose no real threat except from infection, but such catastrophes really have occurred. This goes double for gerbils, which are fast and scrappy, and at least triple for adult rats. It's convenient, and also much cheaper than buying individual live rodents at pet-store prices. Most snakes of commonly-kept species can be conditioned to accept prekilled prey, though the conditioning process is sometimes lengthy and frustrating.
Some snakes simply refuse to eat anything other than live prey.
Never leave a live feeder rodent alone with a snake, especially in the case of tough scrappers like rats. In short, don't invite trouble. Naturally, many of the caveats of this section do not apply to pinky or fuzzy rodents, which are not yet developed enough to injure anything larger than a small insect. However, conditioning a snake to take prekilled pinkies or fuzzies while it is a juvenile may help encourage it to eat dead prey as an adult. The snake managed to knock the mouse's mouth open and drag the teeth over its side while searching for the head.