Continuity mistake: The position of the people while they sit or lie on the beach, before Alex is attacked, changes back and forth between shots throughout this scene. (00:15:10)
Continuity mistake: Throughout the film, there are abrupt changes concerning the position of the sun's shadow, or going from being windy to not, or being overcast to bright and sunny, or where the water is either at a dead calm or pretty rough, all between consecutive shots within a scene. (00:15:15 - 01:21:30)
Continuity mistake: As Brody sits on the shore with Ellen, a councilman approaches. Between shots, Brody's left hand changes position - jumping from his lap to the back of the beach chair in an instant. (00:15:15)
Continuity mistake: When Ellen speaks with Brody at the beach, while worrying about the shark, Michael and other kids get up, and head toward the water. In the next shot, Michael, who wears very distinctive green and orange swimming trunks, jumps into the water (holding a football), and gets his hair and body entirely soaked. Next three shots Harry (and his 'bad hat') sits down and speaks with Brody. In the next shot Michael, with dry hair, passes Mrs. Kintner and is still running towards the water with Sean. (00:15:40)
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: Just before the Kintner boy is attacked, when Chief Brody is sitting on the beach watching the water, he speaks with the old man called Harry. In the close-up shot of Harry the chin strap of his rubber cap hangs down loose at his chest, but in the side shots the chin strap is tucked up at his ear (seen when Harry stands up). (00:16:00)
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 Brody yells for everyone to get out of the water after Alex's attack, the position of all the adults and children as they run differ greatly depending on camera angle, regardless of the ensuing mayhem. (00:17:25)
Character mistake: During one of the shark scares at the beach, Chief Brody is running along the shoreline telling everyone to get out of the water. There are several frames where the Chief and a man with a moustache are at the water's edge. If you look closely you will notice that the man is smiling and laughing and other people laugh as well. (00:17:30)
Continuity mistake: After Alex's attack, there is a close-up of the $3,000 reward sign pinned to the board, as the woman complains, "We won't have any of our regular customers..." in the next shot as she continues to say, "We don't even know that there's a shark around here..." the reward sign on the board has different handwriting and is positioned differently on the board. (00:18:10)
Factual error: Chief Brody is wearing his badge on the wrong side of his chest in every scene. That must have been deliberate for reasons only known to cast and/or crew. A sworn Peace Officer always wears his badge on the left side of his chest, symbolizing that it is over his heart. (00:18:25)
Continuity mistake: As the townspeople make their way into council chambers, we can see Mrs. Taft talking to Chief Brody before she takes a seat. Between frames, her purse strap removes itself from her left shoulder. (00:19:00)
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: In the council chambers, after the Mayor says, "Only 24 hrs," as the people argue in the wideshot a particular area of the chalkboard is visible behind them and it is blank. In the very next close-up Quint, who was not in the previous shot, scrapes the board with his nails, which now shows the large doodle of the shark, that should have also been visible in the previous shot, but was not. (00:20:30)
Revealing mistake: Just as Quint finishes scraping his nails on the chalkboard, the camera begins to move in closer when he takes the first bite of the cracker. On the right side of the screen under Harry's chin, Roy Scheider is ducking down while staring at the camera, as it pans toward Robert Shaw, and Roy then lifts his left hand up, cueing Robert's line. (00:20:55)
Visible crew/equipment: When Quint is doing his speech at the town meeting the camera slowly moves towards him. When the camera passes the man in the grey suit you can see a moving shadow near Quint. Everyone in the room is stationary in this scene apart from the cameraman and film crew. (00:20:55)
Continuity mistake: After Quint scrapes the chalkboard with his nails, in a close-up when he says, "Gonna stay alive and ante up, or gonna play it cheap," the papers pinned to the bulletin board are visible in the room behind him, as well as the chair, etc. In Quint's next close-up, the papers differ with additional pink and blue sheets and the chair is now at the other end of the board. (00:21:20)
Continuity mistake: Throughout Quint's speech in council chambers, the door behind Brody continually opens and closes in alternating shots. (00:21:25)
Continuity mistake: While Quint makes his offer at the town meeting, when he says, "I don't want no volunteers, no mates...," the chalkboard is beside him in this close-up. The doodle of the shark on the board, and the actual wood grain of the chalkboard frame all differ from the previous shots. (00:21:40)
Continuity mistake: Just after Brody flips through the pages of the graphic shark book, Ellen tells him that Michael is sitting in his boat and outside their window the sun is just above the horizon, showing a pretty sunset. Then when Brody rushes to the door to shout for Michael to get out of the boat, amusingly enough the sun is now much, much higher in the sky. (00:23:00)
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.