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.
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: In the scene where Brody blows up the shark, off in the background there is land in some shots and then no land in others. At one point, there is land about half way across the horizon, then there is land across the whole horizon, and then no land, it varies shot to shot.
Continuity mistake: In a deleted scene, Quint walks into a music store to buy piano wire for his fishing reel. The woman behind the counter is giving a young customer a new clarinet reed and says, "It's a number three. It should be softer than the number two you had." Clarinet reed hardness is categorized with one being the softest and five being the hardest, so a three would be harder than a two.
Continuity mistake: When Quint is shouting 'Stand away from those damn cleets,' he is holding a hand gripper on the orca's mast. Then he's near the controls, which is impossible in a split second: no human can move that fast.
Continuity mistake: The word ORCA on the back of the boat continually changes from shot to shot varying from very rusty letters to shiny letters.
Continuity mistake: When Quint slides down the deck towards the shark, there is a shot that shows Brody's legs sliding right behind Quint. However, Brody is still back up in the cabin in the next shot.
Continuity mistake: When the barrel comes over the top of the boat Brody ducks to his left and it just misses him - in the next shot Quint is standing immediately to his right, so he should have been hit by the barrel, knocked out or even killed.
Continuity mistake: At the end Brody throws the diving tank into the shark's mouth with the bottom first. When he shoots the tank it has turned round with the fat end facing out.
Continuity mistake: When Jaws jumps onto the back of the Orca, the Orca tilts to the right. After Quint gets killed Brody goes inside, and the Orca is tilting to the left without sinking anymore.
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.
Continuity mistake: When Sheriff Brody is tossing chum to attract the shark, the cigarette between his lips is not lit but when he backs into the bridge of the boat, there is smoke trailing from the cigarette.
Continuity mistake: When all 3 men are putting the shark cage together for Hooper, and they move the cage over to the side of the boat, Brody is shirtless. Then the next shot where the cage is going into the water, Brody's black T-shirt is back on.
Continuity mistake: When Jaws leaves the pond after the attack its fins go below the water as it approaches the bridge, the scene immediately changes to the bridge, the woman is shouting "shark" and we see the fins go below the water again.
Continuity mistake: When the man gets attacked the long shot shows two of the three boys on top of the upturned boat, then we see the leg sink to the bottom with a trainer on, even though the man was bare footed. Then the camera passes the boy in the water and the other two boys are only just climbing up onto the boat.
Continuity mistake: When the Kitner boy was attacked, the underwater shots show the swimmers treading water in fairly deep water, but the above shots show the kids standing in shallow water.
Continuity mistake: When Quint is up in the crow's nest, Brody tells him "Let Hooper take a turn" (regarding chumming the water). When Quint, while looking down at Brody, says "Hooper drives the boat, Chief", his right arm is across his body and looks to be resting on the safety railing of the crow's nest. When Brody looks up at Quint, his right arm is away from his body and is just holding onto the crow's nest railing with his hand.
Continuity mistake: When the shark is attacking Hooper in the cage, what happened to the the lines to the barrels they have shot into the shark?
Continuity mistake: When Hooper is lowered in the cage, Jaws approaches with the barrels attached, but when he passes the barrels are gone and never return.
Continuity mistake: When jaws jumps on the back of the boat, Quint falls on the floor and the shark's head is 3/4 submerged - in the next shot the head is fully above the water and submerges 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