Continuity mistake: After the cleats are ripped off, the size, shape and characteristics of the exposed area of wood underneath significantly changes in some of the following shots. (01:44:50)
Continuity mistake: When Brody helps the boys pull Michael out of the water his uniform is soaked - much, much wetter than it should have been. In the next shot only the bottom of his pant legs are wet, and in the following shot the wetness of his uniform differs again. (01:03:20)
Continuity mistake: When Hooper measures the Tiger shark's mouth, the people standing around him change between the close-up and the previous and following wideshots. (00:33:30)
Continuity mistake: After Brody throws down the pump, the shark causes the boat to tip. In the following close-up of Quint's hand, the black and red painted gauge panel behind the wheel is visible. The peeled paint, or lack of, on the ledge going round the bridge deck, and on the steering and throttle controls panel, differs greatly in most of the shots of the bridge deck. (01:41:05 - 01:46:40)
Continuity mistake: After Quint receives the rope burn on his hand, the shark creates a huge splash wetting Quint and Hooper. In the following shots the wetness of their clothes and hair varies greatly, particularly Quint. (01:38:00)
Continuity mistake: When the barrel pops up at the stern of Orca, Hooper grabs the boat hook and reaches for the barrel. In the side shot the barrel faces Hooper's right and the homing device is at the top, in the back shot the homing device is gone and in the third front shot the barrel faces Hooper's left. (01:37:10)
Continuity mistake: When the shark enters the Estuary, he passes Sean playing on the sand. After the attack Michael is pulled ashore and there is a close-up of Sean crying. Behind Sean the orange and white stripe cabanas are visible. However, there are no cabanas at the shores of the pond; these cabanas are located at the main beach area. The footage of Sean, with the cabanas behind him, is from the earlier scene of Alex's attack. (01:02:00 - 01:03:30)
Continuity mistake: When the 'shark fin' (boys playing a trick) approaches a woman she shouts, "My God!" and turns to swim towards the family with three children on a yellow raft, surrounded by other swimmers. In the next shot of a man's reaction, he too swims towards the very same family, but this time the children are in different order and no others surround them. (00:59:10)
Continuity mistake: When the two old fishermen are fishing for the shark from the pier, the shark takes the bait and you can see the chain getting pulled into the sea. In the next shot you can still hear the chain being pulled into the sea but if you look on the pier, you can't see any chain being dragged in and the wooden post that the chain is secured to changes into a different position. (00:25:20)
Continuity mistake: In the scene where the shark eats the guy in the red boat in the pond, Brody grabs a red blanket and goes for a brown blanket after exclaiming, "He's in shock," in reference to his son's close encounter with the shark. In the next shot, his wife is laying down blue and brown blankets over Michael. (01:06:05)
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: 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: There are long poles and large hooks clipped to both the starboard and port side of Orca. In quite a few shots all three poles are gone from either side, and in other shots the amount of poles and hooks and their positions change repeatedly over and over again, in consecutive shots throughout their hunt! (01:41:15)
Continuity mistake: The man speaking to Brody on the beach, while Brody is preoccupied with staring at the water, has salt and pepper colored hair, but in the close-up shots facing Brody the man's hair very noticeably differs, as well as his upper body structure and tan. (00:15:40)
Continuity mistake: The chunk of dock that floats in the water, as the shark pulls it, differs from the piece of dock that broke off in the previous shots. (00:26:30)
Continuity mistake: When Quint finishes off his beer and squeezes the can with his hand, Hooper's equipment is visible just behind Quint. Then Brody accidentally unties the cage bars. When he falls back into Hooper's equipment, now it is closer to the door and the lines securing them are entirely different. (01:13:25)
Continuity mistake: As the tanks of compressed air roll towards Hooper, the large silver cage canisters near the ladder are visible. When Hooper carries a tank to the cabin saying, "You screw around with these tanks and they're gonna blow up," there is a long grey cloth (scarf?) lying on one of the canisters. (01:13:40)
Continuity mistake: When the camera is zooming in on Quint as he gives his speech at the town meeting, there is a woman in black and another in blue, seated in the room. In the next shot of people in the room listening to Quint, the woman in blue is in the foreground, but the woman in black who was sitting right next to her, has vanished. (00:20:00 - 00:20:35)
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: 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)
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.