Revealing mistake: In the scene where the shark has Michael cornered in the old, rusted boat; as he's about to use his oxygen tank to rocket up to the surface, the shark breaks through the wall and when it does, a large number of thick tubes can be seen running into the shark to make it work.Clerk13
Revealing mistake: When the shark is rammed by the boat at the end, right before it explodes it is too obvious that the shark is a model. Some signs are: the oversized dorsal fins, its mouth is bent at an unrealistic angle, and it doesn't have eyes.
Revealing mistake: As the boat sinks you can see the rope attached to slow the boat sinking and control how it goes down. (00:10:45)
Revealing mistake: When the shark explodes, in the last shot (from behind the boat) which shows him exploding it is painfully obvious that the boat is only a model and not the real boat from previous shots.