Continuity mistake: At the beach party, when Cassidy and Chrissie make eyes at each other, in the close-up he sits behind certain people including a girl with blond braids and guy in a denim shirt, with long sleeves. However, in the next wide shot, denim shirt guy has his sleeves rolled up and many of their positions are different. (00:02:00)
Continuity mistake: When the guy is standing on the beach in the opening scenes the sunset is covered by cloud. When seeing the sunset from the woman in the sea's perspective the sky is clear with no clouds. (00:02:50)
Continuity mistake: Check out the scene where the girl gets attacked at the start - keep your eye on the clouds and how they move around. (00:03:10)
Audio problem: While Chrissie is being attacked at the start of the film, when her mouth is visible it is not in sync with her screams. (00:04:15)
Revealing mistake: During Chrissie's attack, she clings to the buoy and cries, "Oh my God! Oh God!" In the next shot, as she is pulled away from the buoy, a wire (at about the height of the bell) that shimmers in the moonlight and bounces up and down with the buoy, runs from the buoy towards the right of the screen. It is not visible in any other shot. (00:04:35)
Continuity mistake: In his bedroom, when Chief Brody asks, "How come the sun didn't used to shine in here?" the ashtray and lamp are visible beside Ellen. In the following shots the ashtray and lamp's electrical cord noticeably keep changing positions. When he walks out of the bedroom, something (mug?) appears on the desk near the window that wasn't there in the previous shot. (00:05:20)
Continuity mistake: When Michael walks into the kitchen, he holds up his bloody hand and exclaims, "I got hit by a vampire!" In the next wideshot the blood on his raised palm differs. (00:06:00)
Continuity mistake: When Brody questions Tom about Chrissie's disappearance, Brody turns his head away from Tom between frames, just as they hear Hendricks' whistle. (00:08:00)
Other mistake: On the death certificate for Chrissie, the shark's first victim, the date of death is July 1st. But later, on the reward paper posted by the boy's mother, it says that the date of Alex's death was June 29th. Alex died after Chrissie, not before. Also, the form refers to the coroner as the "corner," and Jun 29th 1974 was a Saturday, not Sunday. (00:09:05 - 00:18:10)
Character mistake: In the beginning of the movie, Chrissy goes swimming on the night of July 1. Her remains were found the next morning on July 2. The police report that Brody types up states that the incident happened at 11:50 p.m. On July 1 and that Chrissy's remains were found at 10:20 p.m. On July 2 and not in the a.m. As the movie shows. Also on the police report, it states that Chrissy was removed to the "CORNERS OFFICE" and not the coroner's office. (00:09:30)
Visible crew/equipment: After Brody buys the sign supplies, when Hendricks shows up Brody places the box in the front seat, and as Hendricks tells Brody about the Boy Scouts, pay attention to the left window across the street, where we can see one of the local residents holding a camera and looking out the window facing the location shoot, taking pictures of the actors and film crew. The filming took place at the corner of Main St and S. Water St, Edgartown. (00:10:50)
Continuity mistake: After buying the sign supplies, Brody drives away and as the Mayor calls out to Brody, Hendricks walks over. In the first shot certain people are walking about; however, in the next shot as Hendricks and the Mayor speak, a boy suddenly appears standing in the crosswalk, the positions of signs, etc., differ, and of course the shadows cast are entirely different. (00:11:15)
Continuity mistake: After Brody walks out of the store with a box of sign supplies, wood stakes, and boards, Brody dumps everything into Hendricks' arms, with the points of the five wood stakes facing Hendricks' right side. When Brody drives away as Mayor Vaughn calls out to him, Hendricks walks over with his arms full, but all the stake points now face his left and the supplies box is turned around, note its printed sides. (00:11:15)
Continuity mistake: When Brody waits to board the ferry he says, "Charlie, take me over to those kids, will ya," and there's a painted board with 'Amity' attached to the ferry base. However, when they reach the other ferry landing the board with 'Amity' is gone, in sloshing water (even more visible in a deleted scene). It's the same side of the ferry, note the ferry Captain is stationed at the permanent helm at only one side. The short haul Chappy Ferry On Time scow was the stand-in for the fictitious Amity ferry. (00:11:40)
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: When Mayor Vaughn, Hendricks and the others join Brody on the ferry, as they reach the other side of the harbor the coroner's front leans on the car, as he faces the Mayor and Brody. However, in the next shot the coroner's back now leans on the car, as he faces the opposite way. (00:13:25)
Audio problem: Alex asks his mom if he can still go in the water, and when she says, "Just ten more minutes," although it is a side shot of her face, it is easy to see that her mouth movements are not in sync with her words. (00:13:50)
Continuity mistake: Before Alex's attack, the guy who plays with his dog Pippet on the beach wears a bright yellow Izod polo shirt with straight hemmed sleeves, in all of his close-ups. However, in all of the wideshots the polo he wears is pale yellow, with shorter sleeves that have the classic rib-knit sleeve openings. (00:14:10)
Continuity mistake: When Brody sits on the beach watching the crowd in the water before Alex is killed by the shark, he wears a watch on his wrist which disappears a few shots later when he believes he saw something. (00:14:48)
Continuity mistake: While Brody watches the woman in the water, before Alex is attacked, there is a blue and yellow raft in the cabana behind him. In the close-up of his face, just before Harry's black capped head pops out of the water, the raft is gone. Then when Ellen massages Brody's neck the raft is back. The cooler and other assorted items change position between shots as well. (00:15:00)
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.