Other mistake: Near the beginning of the film, Carter asks Tom how high the fences are, then he tells them to make them higher, and Scoggs confirmed they were raised, but you can see that the fences never get any higher.
Visible crew/equipment: As Preacher and his parrot are about to go up the stairs to a higher level, you can see a wire attached to the parrot. (00:43:05)
Revealing mistake: As one of the lab crew is showing Tomas Jane the suspended tiger shark you can see a horizontal line in the water in the background. this is the edge of the water tank used to film the exterior scenes (mentioned in DVD extras).
Answer: The shark was waiting for them to come that way. It'd already smashed the escape pod. All the shark did was to lure in the water until someone got near enough for it to grab them. The sharks were unnaturally intelligent, so it seems fair that this was a part of their plan.
Mortug