What has an opossum ever done to you? What about a raccoon? My dogs, 3 vicious, blood-thirsty Boxers have killed two raccoons, an opossum, a ground hog and a bazillion moles...all within my fenced 3 acres.
Cowgirl is right on point. Prey drive...many NICE dogs have it. I'm not really a Pit fan either but any dog can kill another animal and sometimes something as simple as curiosity can turn out deadly. The dogs take in interest in a "critter," the critter runs and the game is on. There's a huge difference between killing a goat/another animal and killing a person.