Revealing mistake: While Hooper is below in the cage, he sees the shark nearing and up on deck as the barrels speed closer, the black triangular device attached to their lines is clearly visible, right in front of the barrels. The device pulls the barrels, not the shark. (01:53:15)
Continuity mistake: When the shark is swimming towards the shark cage, it shows the three barrels above the water. If Quint shot them in different parts of the shark's body, they would be spread out and in different places, but the barrels are stuck together. (01:53:25)
Revealing mistake: When Hooper is in the cage the regulator hose is to Hooper's right (viewer's left when facing him). However, when the shark first appears and passes Hooper, in the shot facing him the hose is now to Hooper's left (viewer's right), and the word "repeater" on the poison shark dart is also backwards. This is a flipped shot. (01:53:30)
Continuity mistake: When Chief Brody and Hooper tie the ropes to the stern cleats, Quint shoots a harpoon under the shark's mouth. When Hooper is in the shark cage, look at the shark's mouth when it passes by. There is no harpoon there. (01:53:35)
Continuity mistake: When Hooper is lowered into the water in the shark cage, in the following shots the ring he is wearing on his left hand vanishes and reappears in a few shots, such as when he drops the poison shark dart. (01:53:50)
Visible crew/equipment: Just after the shark's first surprise attack on Hooper's cage, bright blue equipment is visible just past the cage, as the shark swims away. (01:54:10)
Continuity mistake: After the first shot of Hooper's shark dart falling, in the next shot of the shark swimming away, the cage top is wide open, yet in the previous shots and following close-up the top of the cage is closed, until Hooper actually opens it. (01:54:15)
Continuity mistake: When the shark slams into the cage and makes Hooper drop his weapon, it shows the underside of the shark; look at the its mouth. When the shark is about to slam into the cage again its mouth isn't the same size as it was before. You can tell that they used a real shark when they showed the underside. (01:54:15)
Revealing mistake: As the shark pushes his face into Hooper's cage, in a very nice close-up of the underside of his pectoral fin the large amount of peeled paint is quite visible, as it is in other shots of other areas of his body. Then in another shot at the same angle, just before Hooper escapes the cage, the paint job is perfect. In some other close-ups the shark's outer flesh creases deeply, because of its hollow interior, when pushed up against other surfaces. (01:55:00)
Revealing mistake: While the shark's face is up close and personal in the cage with Hooper, the equipment under the shark is visible as the camera pans back and is visible again in following shots. In the shot just prior to Hooper swimming away the device is quite clear. (01:55:00)
Continuity mistake: The damage to the bars of the cage and the top canister changes, and is quite different once Quint and Brody hoist it up. (01:55:05)
Continuity mistake: After the Orca breaks down for good, Hooper goes into the shark cage to try to kill the shark. The shark proceeds to completely trash the bars on one of the sides. After Hooper escapes to the sea bottom, the shark is attacking the top of the cage, but the bars are now intact. [Extra info: The scene with the bars intact actually shows a very real shark that got caught in the line(s) holding the intact cage. When they raised the cage it was still caught in the line(s). They inserted this footage after the scenes with Hooper and Bruce where the cage got trashed.] (01:55:20)
Continuity mistake: When Quint is telling Brody and Hooper about his body loses during the past, he pulls out a partial denture. In the final scene on the Orca, Quint is shown without this denture, but when he is being eaten by the shark and screams in pain, his teeth are complete again. (01:56:20 - 01:57:20)
Continuity mistake: When Quint stops cranking to hoist up the cage, in the first shot the large canister is below the deck rail, but in the next shot the canister is well above the rail, right beside Brody. (01:56:30)
Visible crew/equipment: After hoisting up the damaged cage, when Quint walks over to stand beside Brody in the close-up the reflection of a male crew member's head is visible in the window, behind the ladder, until Brody lets go of the line. The crew's moving shadow is also visible under the cabin window, just after Quint passes it. (01:56:40)
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. (01:56:50)
Continuity mistake: The damage to Orca's stern changes back and forth, between shots. For instance, when the shark first comes aboard the entire transom is torn off, splitting the deck and side rails. Yet, just before the air tank rolls onto Quint's hands, part of the transom is back and the deck rail is whole again. (01:56:50)
Continuity mistake: When the shark is boarding the boat, Quint and Brody are on their backs in the cabin beside the table. It is clearly visible that they are lying on the very solid floor with the hatches in perfect condition, despite the visibly massive damage to the floor and hatch when the engine room exploded. (01:57:00)
Continuity mistake: The position of Brody's gun holster, along the wide belt changes between shots, when he tries to hold on to Quint's hand. This occurs in other shots as well. (01:57:00)
Continuity mistake: While Quint slides towards the shark and subsequently munches on him, then leaves, the articles and debris on the deck noticeably change between shots, regardless of the water splashing about. (01:57:05)
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