Revealing mistake: In the absolutely brilliant boat scene towards the end of the film, there is a medium shot of the rear of the boat when Jaws comes right out of the water. If you look carefully under the shark model as it leaves the water, you can see the mechanical wheel they used to maneuver the model.
Continuity mistake: Check out the scene where the girl gets attacked at the start - keep your eye on the clouds and how they move around. (00:03:10)
Continuity mistake: While Brody watches the woman in the water, before Alex is attacked, there is a blue and yellow raft in the cabana behind him. In the close-up of his face, just before Harry's black capped head pops out of the water, the raft is gone. Then when Ellen massages Brody's neck the raft is back. The cooler and other assorted items change position between shots as well. (00:15:00)
Factual error: When Hooper examines the remains of the swimmer he lifts up what is left of the woman's left hand and forearm. The blood and flesh are a bright colour. Blood and flesh discolour very quickly on a dead body - these bits should be a lot darker and the flesh a lot paler and dark bluish in colour.
Revealing mistake: The ropes from the two barrels attached to 'Bruce' the shark are tied to the stern cleats, but then Bruce pulls on the ropes and starts to drag the boat sideways and nearly submerges the stern of the boat. As the boat is being pulled sideways by the ropes, they are both shown to have quite a bit of looseness, or slack in them. How can the boat be pulled like that if the ropes are not taut? (01:44:05)
Audio problem: When the old fisherman yells at his friend to swim faster and not to look back, his mouth movements aren't consistent with what he is saying. (00:25:55)
Other mistake: When the boy gets attacked on the lilo and everyone is told to get out the water, the group of boys are standing just in front of the pool of blood. The water is too shallow for a shark of that size to swim in without it being seen.
Character mistake: In the beginning of the movie, Chrissy goes swimming on the night of July 1. Her remains were found the next morning on July 2. The police report that Brody types up states that the incident happened at 11:50 p.m. On July 1 and that Chrissy's remains were found at 10:20 p.m. On July 2 and not in the a.m. As the movie shows. Also on the police report, it states that Chrissy was removed to the "CORNERS OFFICE" and not the coroner's office. (00:09:30)
Continuity mistake: When the shark is harpooned to some rope, Brody & Hooper tie the rope to the stern cleats, causing the boat to be dragged backwards. Quint gets a machete to cut the rope to limit the boat's damage. At this point the sea is somewhat choppy. He throws the machete making it stick into the edge of the boat. The sea in the background is now completely calm. (01:44:25)