Continuity mistake: When the Antereans go into the sea for about the second time I think, Jack stays on the boat and starts playing about with the machine and makes it go off. When it does he drops a load of sweets or nuts out of the bag he was holding, but when the camera cuts away then cuts back there are no nuts or sweets on the floor.
Deliberate mistake: David spots the boat with the old folk on and runs around the harbor, down the jetty and jumps towards the dive boat as it leaves the jetty. He doesn't jump very high and you can see he would miss the rail on the boat. In the next shot, a (larger) stunt double is shown leaping high in the air onto the boat and, of course, catches the rail.