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)
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)
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)
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 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)
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)
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)
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)
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 Chrissie goes swimming at the start of the film, we see the moon in the distance. However, when we see Chrissie from the shark's point of view under the water, the moon is directly above Chrissie.
Continuity mistake: In the famously later on added scene Ben Gardner's suddenly emerging head scares the hell out of Hooper the diver (as well as any viewer). What diminishes the effect is that the second close-up of the head looks nothing like the first, much creepier one.
Continuity mistake: When Quint comes out the cabin with the life jackets the boat is listing to our left as we look at it from the back. When he asks Hooper about the injection and the cage the boat has levelled off, and stays that way until they try and lift the cage back up.
Continuity mistake: Near the end, when Quint is struggling to get away from the shark, the nearby cans on the deck change between shots.
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.