Factual error: When Hooper sees the hole in the hull of Ben Gardner's boat, he uses his knife to pry out the shark tooth. The tooth is located at the bottom of the hole, with its flat root side stuck deep in the wood and its pointy side facing up. It is completely impossible for the shark's tooth to become wedged in the wood this way, while he takes a nice bite out of the wood hull.
Continuity mistake: At the harbor, just as Brody asks, "Help me get those guys out of the boat, will you?" in the wideshot there are five men standing on the dock and three standing in the boat. Then in the next close-up, there are four on the dock and four in the boat. The one in a black/white check shirt is now at the end of the dock and the one in a black rain slicker, that was standing on the dock, is now suddenly standing in the boat below, at its stern.
Continuity mistake: Quint slams the machete into the wood beside the side cleat, and rigging lines. However, when the shark joins them aboard the boat and Quint is sliding towards its mouth, the machete's position changes - it is farther down towards the stern, note the black anti-slip mats.
Revealing mistake: When the shark takes the fishermen's bait, the attached chain pulls one corner piling at the corner of the small dock. When the dock gives way in the wide shot, another line around the second corner piling visibly pulls it as well, in order for the dock to break apart effectively for the stunt.
Continuity mistake: When Brody and Hooper first arrive at Quint's place, Quint goes to pour the drinks, and beside him are windows with shades. There is a fish that hangs over the window beside Brody and the window upstairs, above Quint, is open. In the following shots positions of the roll shades, towels, etc., differ. Then when Quint climbs the ladder a bunch of rope now hangs beside the mirror, there is a small net that hangs with the fish above the window, and the window upstairs is now closed.
Continuity mistake: There is a scene where Chief Brody and his wife are talking about their son's birthday present. She says that he probably won't go in the water after what happened yesterday (the attack on the Kintner boy). The next day is when the shark is caught and Hooper makes a comment about the shark's digestive system being very slow and anything he's eaten within the last 24 hours would probably still be in there. From the earlier scene it would make it 48 hours since the Kintner boy was killed.
Continuity mistake: When Hooper climbs into the cage he is not wearing fins, yet when he is lowered in the cage, in the very first shot underwater, he is wearing fins. In the following shots he is not wearing fins, but after the shark destroys the cage and he swims to the bottom of the ocean, he is wearing fins once again.
Visible crew/equipment: After losing Quint, Brody is in the flooded cabin as the ship tips. Just before the shark bursts in, there is an exterior shot looking into the cabin through the window with the shards of glass. A crew member wearing a jacket and hat is visible in the reflection of the triangular piece of glass, at the top right of the screen.
Revealing mistake: After Hooper's comment, "He's working his way up to us," Quint rushes to the stern and shoots another line into the shark. In a very tight close-up of the shark's gills it is very apparent that they are just wide carved ridges, with no slits whatsoever, to even attempt to give the illusion that they are real, like in other great shots of Bruce.
Visible crew/equipment: After Quint walks on deck and tosses the life vests to Hooper and Brody, Quint asks, "Hooper, what exactly can you do with these things of yours?" Just as Hooper turns around, the clear moving reflection of a boom mic and pole are visible on the glass of the door to the cabin, just behind him.
Continuity mistake: At the beach party, when Cassidy and Chrissie make eyes at each other, in the close-up he sits behind certain people including a girl with blond braids and guy in a denim shirt, with long sleeves. However, in the next wide shot, denim shirt guy has his sleeves rolled up and many of their positions are different.
Revealing mistake: As the shark jumps on to the back of the boat, a metal wire is visible from the shark's fin. It's not the barrels because it disappears in the next shot.
Continuity mistake: Hooper wears rimless eyeglasses, with the arms either attached at the upper corners of the lenses or at the sides of the lenses. If this didn't happen between shots within the same scenes, it could be presumed that Hooper has two different pairs of glasses and switches between the two, but they do indeed change between shots, such as when Mrs. Kintner slaps Brody, or even later, on the Orca.