Continuity mistake: Before Quint meets his fate, we see him lose grip with Brody's arm. But in the following shot Quint is still holding onto Brody's arm despite having let go just a moment ago. (01:57:05)
Revealing mistake: Towards the end of the movie, when Quint is practically bitten in half, the mechanical shark's rubber teeth bend as it bites down, and they also bend when the shark bites down on the tank. (01:57:10 - 01:58:05)
Continuity mistake: When Quint gets bitten by the shark, he spits out blood. The blood on his face and chin noticeably changes in consecutive shots. (01:57:10)
Revealing mistake: When the bottom half of Quint's body is in the shark's mouth, Quint's fake belly shifts around where the shirt is open and the edge is also noticeable under his shirt. (01:57:25)
Continuity mistake: In Quint's final scene, the bandana headband slips off Quint's head twice and then reappears back on his head twice, between shots. First, when the shark begins biting down on him and a few moments later when the shark is thrashing Quint from side to side. (01:57:25)
Revealing mistake: While Quint is in the shark's mouth, the comfy white cushion is visible under his back, protruding from the shark's mouth. (01:57:30)
Continuity mistake: During Quint's attack, as the shark's biting down on his legs, Quint's bare hand is grabbing the shark's snout. Subsequent shots show Quint wearing gloves as he's devoured. (01:57:35)
Revealing mistake: After the shark disappears, with Quint in its mouth, in the next shot facing Brody the door to the cabin closes. The wire attached to the door, leading offscreen to the right, is clearly visible. (01:57:40)
Continuity mistake: After the shark leaves with Quint, Brody is in the flooded cabin as the boat starts to tip and the stove is behind him. The large metal side panels are fitted in the grooves between the lid and base. However, when the shark crashes through the window the panels are gone and the lid to the stove is closed. (01:57:45)
Continuity mistake: As the shark bursts through the port side windows, the remaining port side wall and window frame around it keeps changing between shots - from an entirely broken frame to a partial intact frame, and so forth. (01:57:50)
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. (01:57:55)
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. (01:57:55)
Continuity mistake: When Brody is in the flooded cabin as it tips, at the start of the shot where the shark makes its smashing entrance, we actually hear Brody's loud footsteps on wood, as we see his waist and legs run from aft to forward in the cabin; though in the previous shots Brody is more than waist level in the water, already standing towards the bow. (01:57:55)
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. (01:58:00)
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. (01:58:00)
Factual error: After the shark tries to attack Brody on Orca, it swims backwards out of the cabin, just as it does in other shots. No shark can swim backwards. (01:58:05)
Continuity mistake: When Brody is on the mast of the Orca with Quint's rifle, preparing to shoot the shark, the shark emerges from the water and there is blood on the end of its nose, but after a quick cut to Brody, we return to the shark and blood has disappeared. (01:59:20)
Continuity mistake: When Quint and co. are tracking the shark, they use harpoons tied to barrels to tire the shark. When the shark is approaching Brody, who sits on the foremast waiting to shoot it, the surface of the water is visible behind it and the barrels are gone in two shots. The barrels are also gone when the shark blows up. (01:59:40)
Continuity mistake: When Brody fires the last shot at the air tank, in the next close-up of the shark, the tank lies parallel to its body deep within its mouth, with only the base of the tank visible between its teeth. However, in the next wide shot, the tank lies perpendicularly in its mouth, with the pressure knobs at its right. (02:00:10)
Continuity mistake: When Hooper first gets introduced in the movie on the pier, greeted by a fisherman, you notice in the background a man going down a ladder. Only for the camera to cut back to Hooper with the same man going down the same ladder again.
Chosen answer: As mentioned in the movie, the posion was in the needle and the shark's hide was too tough for the needle to penetrate. Hooper had to go in the water so that he could get the needle into the shark's mouth, where the flesh was less tough.
Kevin Howard