Revealing mistake: When the shark bursts through the window of the cabin, in each of the shots facing Brody, including when he shoves the air tank into the shark's mouth, the glistening water is visible in the window's reflection behind Brody. The shark's reflection is never seen behind Brody, despite the shark's massive size in the small cabin. Bruce must have had the day off during Roy Scheider's takes.
Continuity mistake: Quint embeds his machete into the wood at the side of the boat, but in the following wideshot the machete is gone. Then as Orca starts to move, when Hooper says, "He's chasing us, I don't believe it," the machete is back. But when the shark leaps onto the boat the machete is gone again, and then as the shark devours Quint the machete is back for him to grab, so he can valiantly stab the shark.
Continuity mistake: When Hooper gets his gear from below, after the explosion in the engine room, he runs to the deck passing Quint using the fire extinguisher. The camera pans from Brody, who stands on the bridge deck, to Hooper right below him. So where exactly is the tall iron ladder that leads up to the bridge deck in this shot? It should be behind Hooper, in front of the window, but it's gone. Don't fret, it's back in the following shots.
Visible crew/equipment: When the fishermen start out on the hunt, Ben Gardner appears in a close-up leaning on the windshield at forward deck, while talking about how stupid some of the others are. In the next wide shot of the boats, Ben's green boat is towards the left of the screen, and the large reflector screen and camera, that are mounted to the bow of his boat, are visible in front of the forward window where Ben is seen in the previous shot.
Continuity mistake: At the scene just after the fake shark scare, the real shark shows up at the pond area of the beach. As the lifeguard in a small boat reacts to everyone's panic, the shark tips over the boat then appears underneath him to tear his leg off. We watch as it sinks slowly to the bottom. You can plainly see that the lifeguard is barefoot in the boat. The severed leg has a tennis shoe on.
Revealing mistake: In the scene in which the two men are fishing for the shark with the roast and inner tube, watch the amount of chain that is pulled off of the pier. Not only do numerous feet of chain go out but there are already many feet in the water connected to the tube. When the pier gets pulled into the water and the shark makes the turn to chase after Charlie, watch how close the pier is to him. With the amount of chain that was let out, the shark would have been well past Charlie and the shark probably would've beached itself.
Continuity mistake: When the shark bursts into Orca's cabin and tries to attack Brody, in the shots facing the shark, at the right of the screen is the forward window. The previously shattered glass (from the yellow barrel) is now perfectly intact within the window frame, and the large wood cabinet below that window is gone. The glass is shattered once again, when Brody climbs out of the cabin, through the window beside it.
Character mistake: On the death certificate for Chrissie, the shark's first victim, the date of death is July 1st. But later, on the reward paper posted by the boy's mother, it says that the date of Alex's death was June 29th. Alex died after Chrissie, not before. Also, the form refers to the coroner as the "corner."
00:09:05 - 00:18:10
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.
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.
Revealing mistake: Just as Quint finishes scraping his nails on the chalkboard, the camera begins to move in closer when he takes the first bite of the cracker. On the right side of the screen under Harry's chin, Roy Scheider is seen ducking down while staring at the camera, as it pans toward Robert Shaw, and he then lifts his left hand up, cueing Robert's line.
Revealing mistake: When Quint is gone, the shark bursts through the window of the cabin surprising Brody and in its second close-up, with its jaws wide open, the shark's head moves from left to right of the screen. As it does, the aft side of the cabin set is visible on the left, with the wall conspicuously missing and then at the fore side of the cabin, the window frame is not complete.
Revealing mistake: When Hooper encounters Ben, the shape and size of the hole in the hull of Ben Gardner's boat, as well as the paint stripes on the hull, all change in this shot. (The close-ups of Ben's appearance were shot later in pick-ups after principal photography wrapped.)