It's a lot more common in the wild than one thinks. Lions, tigers, wild dogs, alligators, fish, sharks, baboons, birds, hyenas, worms, bears, etc all eat animals that are still alive from time to time. Animals want to conserve as much enery as they can. As long as the prey is debilitated or not attracting other bigger predators, they'll eat it even if it is alive. Nature is really brutal when you get down to it.