Visible crew/equipment: In the scene where Brody approaches the group of teenagers on their smashed boats, the angle cuts to show Brody approaching seen as if from Cable Junction. At this point, there is a huge mistake. The teenagers' boats are clearly visible in the foreground, the kids have all completely vanished, and you can spot the cameraman standing on the boats quite clearly.
Continuity mistake: When Brody thinks he spots a shark, he rings his bell, then begins to descend the watch tower. In one shot you can see a woman with blonde hair, sitting on a beach-chair, at the bottom of the watch-tower. In the next overhead shot, as Brody runs across the beach, the same woman now suddenly has an orange hat on. (00:44:50)
Revealing mistake: When the teenage guy is getting attacked by the shark, the shark slams him up against the boat. He attempts to climb back on the boat and the shark pulls him down and the guy rips some wood from the edge of the boat. You can see the cut away part of wood that will be ripped off before he actually rips it off. (01:11:05)
Revealing mistake: There's one bit where we see the shark slamming into a boat and gliding along the side with its mouth open. Not only does the shark's latex mouth bend beneath the snout, narrowing from pressure, but within the mouth you can clearly see yellow hydraulic tanks to open the mouth. (01:22:05)
Continuity mistake: When the shark is attacking the catamarans with the teenagers aboard, in one shot you see Andy fall backwards, still on the catamaran, and he is barefoot. He is then knocked in the water, and when his friends pull him back out of the water on, he now has white trainers on. (01:20:10 - 01:21:15)
Continuity mistake: When Tina is running away from Eddie in the building on the beach, you see that the building is casting a huge shadow across the beach. But when it cuts to the next shot in which they are running past all their friends, there is no shadow being cast on the shore from the building. (00:26:35)
Audio problem: When the helicopter lands and the teenagers cheer you can hear dialogue from later in the film in the background. Several times you hear "Sean, catch the rope." which they yell later in the movie.
Continuity mistake: In the scene when Chief Brody, his wife & deputy come across the sail boat named "Tina's Joy", they find Tina in it, and during this scene Chief Brody's jacket is placed on Tina's shoulders. The Chief then leaves the sailboat in search of the other teens. Later scenes show the Chief wearing this jacket when in fact he left it with Tina.
Continuity mistake: At the end of the movie when the Chief has killed the shark, you see his son Shawn cheering, with his hair completely wet and messed. By the time the Chief paddles over, Shawn's hair is now perfect; dry, and combed neatly...
Visible crew/equipment: When Brody is checking out his reflection in the small kitchen mirror, he turns around and his wife walks through the doorway into the kitchen. Above the doorway you can clearly see the whole boom mike, pole and all, which is quickly swung up out of view. (01:07:15)
Audio problem: When the shark breaks the katamaran and most of the teens fall into the water by Cable Junction, one of the girls can be heard screaming in the underwater shot of the shark. That is perhaps fine, but the sound of someone screaming as heard under water continues over a few clips from above the surface.
Revealing mistake: After Terry has been taken by the shark, her mum stops the speedboat, and starts calling for her. Then the shark starts swimming over to the boat. In a following side shot of the boat, just before the shark slams itself into the speedboats side, you can see a thick line attached to the front of the speedboat, which wasn't there previously, which is probably used to tow the boat to something off screen. (00:21:10)