When Jackson is polished off by the main shark at the mini-sub pool, you'll notice that he steps off the side of the raised ledge of the pool during his little speech. He then gets eaten. But the ledge that he steps off has suddenly moved so that the shark can slam its head to the floor in order to get Jackson and drag him back into the murky depths to be torn to shreds. You can tell this was necessary for the surprise attack to work, but they should have thought more about leaving the gap on the set in the first place.