I'm surprised this kind of thing doesn't happen more often. Orcas are extremely intelligent predators that eat seals/sea lions, even other whales that we keep up in tiny pens and force to do circus tricks day in day out. They're not dogs, and I think that sometimes the trainers get complacent and forget that they are dealing with extremely dangerous, wild animals that could eat them in one bite. It's a shame that someone died, and certainly terrible that it happened in front of a crowd full of kids, but she ought to have been a little more careful.
