Continuity mistake: In the council chambers, after the Mayor says, "Only 24 hrs," as the people argue in the wideshot a particular area of the chalkboard is visible behind them and it is blank. In the very next close-up Quint, who was not in the previous shot, scrapes the board with his nails, which now shows the large doodle of the shark, that should have also been visible in the previous shot, but was not. (00:20:30)
Continuity mistake: When Hooper and Brody tie off the stern cleats, the amount of line, and the way the lines are wound round the cleats, varies in the following shots. (01:42:35)
Continuity mistake: In his bedroom, when Chief Brody asks, "How come the sun didn't used to shine in here?" the ashtray and lamp are visible beside Ellen. In the following shots the ashtray and lamp's electrical cord noticeably keep changing positions. When he walks out of the bedroom, something (mug?) appears on the desk near the window that wasn't there in the previous shot. (00:05:20)
Continuity mistake: While Brody is in the flooded cabin, before the shark joins him, in the shots facing the aft cabin wall a few things are very different. The wood paneling on the entire wall, the porthole window beside the door, the ceiling and the black fire extinguisher holder all differ, and the round fixture that was screwed into the wall is gone. Also, visible through the window, the permanent ladder is positioned differently and things hanging in front of the window differ from the previous shot. (01:49:00 - 01:57:40)
Continuity mistake: Throughout the film, there are abrupt changes concerning the position of the sun's shadow, or going from being windy to not, or being overcast to bright and sunny, or where the water is either at a dead calm or pretty rough, all between consecutive shots within a scene. (00:15:15 - 01:21:30)
Continuity mistake: When Quint shouts for Hooper and Brody to get their gloves on, in the wideshot Hooper starts to slip his left hand into his left glove. However, in the close-up, he just starts to put his right hand into the right glove. (01:17:40)
Continuity mistake: When Quint is wearing the bandana round his head, the design showing and thickness of the bandana keeps changing in consecutive shots. (01:36:50)
Continuity mistake: After the two barrels are tied off, there is at least twenty feet of line between the barrels and where it disappears into the water. When the next harpoon is shot (the barrel shatters the cabin window) and the shark pulls Orca, that last barrel trails way ahead of Orca, its taught line being extremely shorter than the lines leading to the two other barrels, though the shark pulls them at the same time. However, once the cleats break off, the length of the three lines are identical in length. (01:44:15)
Continuity mistake: When Hooper removes the pump from the locker, in the close-up Quint takes the pump with his empty hands and gives it to Brody with both hands. However, in the wideshot he is holding the machete in his left hand, as he gives Brody the pump. (01:45:30)
Continuity mistake: While Brody and Quint are talking in the cabin, just after Hooper sticks his tongue out at Quint, the books on the shelf are fallen over on their sides. However, in the next shot when Quint walks out on deck, the books are visible behind him and now they're upright. (01:19:45)
Visible crew/equipment: After spotting the shark, which Quint declares is a twenty five footer, Brody asks, "How do we handle this?" and the crew's swaying vessel is visible in the reflection on the starboard windows. (01:22:20)
Continuity mistake: Just as Quint shouts, "You may be a big yahoo in the lab, but out here you're just supercargo..." and when he asks Brody to unbuckle him, the cleat at the stern has plenty of line wound round it and there is a red cup beside it. However, in the previous and following consecutive shots within this scene, there is no line and no cup. (01:17:50)
Continuity mistake: On the Orca near the end of the film, there is a shot of Quint aiming the harpoon gun. In this shot the harpoon gun is high, but in next shot he is shooting from the hip. (01:39:20)
Continuity mistake: While Quint leads the shark into the shallows, Brody asks, "Have you ever had a Great White do this?" and Hooper is beside the foremast holding one of the rungs, directly under the crow's nest. However, in the next shot, he stands at the edge of the bridge deck, beside the rigging. (01:47:25)
Continuity mistake: After Quint states that it's a 25-footer, he rushes below deck and when he comes up with the harpoon case, the gauges on the panel to his left are visible. When he answers the call from Amity Point light station, there is a new large black knob attached the corner of the panel, that was not there before. The paper mess at the top of the panel differs as well. (01:22:25)
Continuity mistake: The position of the people while they sit or lie on the beach, before Alex is attacked, changes back and forth between shots throughout this scene. (00:15:10)
Continuity mistake: In the scene where Hooper visits Brody's home, he brings two bottles of wine. Brody pours himself a large measure, and then gives his wife and Hooper some. If you look at the bottle a) it seems rather full for the amount he's just poured, and b) the level changes from shot to shot. Sometimes it's above the label, sometimes below.
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)
Continuity mistake: In the scene where Hooper is measuring the bite radius of the Tiger shark, he puts his measuring tape away more than once. (00:33:30)
Continuity mistake: At the end when Brody is up in the crow's nest of the Orca waiting for Bruce to get close enough for him to shoot the tank in Bruce's mouth, notice that the crow's nest is sinking much faster than Bruce is moving towards him. At these rates, the boat would have fully sunken before the shark got close enough.
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.