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.
Revealing mistake: Just after the first shark attack, Chief Brody and his deputy discover the beached remains of the nude swimmer. As Chief Brody hesitantly approaches the grisly scene, the camera cuts to a close-up of a mutilated female arm and other viscera, covered with a creeping cluster of small saltwater crabs. Inexplicably, a single crab falls out of thin air on the right side of the screen to join the others. A moment later, Chief Brody arrives at the scene, in the background. Obviously, a film crew member dumped a bucket of live crabs onto the body parts for this shot, but poor editing allowed one of the animals to be seen falling onto the pile.
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 tries asking the fishermen about a restaurant or hotel on the island, he makes a motion with his right hand. But between shots, his hand grabs onto the wood piling. (00:29:10)
Character mistake: When Chief Brody is talking to Mayor Vaughn on the ferry, before he says "I appreciate it I'm just reacting to what I was told" he calls him "Harry" when his real name is Larry. (00:13:10)
Continuity mistake: At the hospital, where Larry waits for Brody to approach, Larry quickly moves his left hand away from the front desk between frames. (01:04:50)
Revealing mistake: When the shark's jaws come down on Quint's stomach, look carefully and you can see Robert Shaw using his hand to push the shark's nose onto his stomach.
Other mistake: The five yellow barrels are not on the Orca when they are getting ready to leave shore. When Quint begins singing, goes and stands at the cabin door, you can see through the front windows that the barrels are not there. With the Orca leaving just moments later, they should have already had the barrels on board. (01:07:30)
Continuity mistake: Before Alex Kintner is attacked, Sean Brody is shown sitting on the beach singing. After Alex is attacked and people are running out of the water, Sean can be seen standing on the beach, and in one shot, Chief Brody can be seen grabbing him. But a couple of seconds later, Sean is shown sitting on the beach in the same spot he was before, as if he hadn't moved. (00:16:55)
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.
Character mistake: When Hopper is in the cage you can tell it isn't him by the size of the scuba tank on his back and size of that kill stick he was going to use. The tank and kill stick are almost as tall as the person in the cage. When on deck and loading into cage in scene before that the items aren't that tall.
Other mistake: Two errors when Hooper is at the helm...the first is Quint yelling at Hooper "starboard, ain't you watching?"the shark is actually running from the port side of Orca. The second is when Quintbtells Hooper to head SSE...Orca turns to starboard while moving ahead...a SSE course would be a turn to port.
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.
Visible crew/equipment: As Hooper says the shark is "back for his noon feeding", you can see the camera and lighting reflected on Brody's glasses.
Revealing mistake: Towards the end, before Quinn is eaten, the shark is "chasing" the boat with 2 barrels. You can see the wire from the boat dragging the barrels off to the right side of the screen.
Revealing mistake: As Quint smashes the radio, then when Brody yells at him, nearby land is reflected in the windows behind them. There is no land in sight both before and after this scene.
Answer: Possibly a scar from having his appendix removed, I've been told.
The appendix shot is Brody - he is feeling inferior as the other two share tales of the sea and the only scar he has is from his appendix being removed.