Continuity mistake: Hooper wears rimless eyeglasses, with the arms either attached at the upper corners of the lenses or at the sides of the lenses. If this didn't happen between shots within the same scenes, it could be presumed that Hooper has two different pairs of glasses and switches between the two, but they do indeed change between shots, such as when Mrs. Kintner slaps Brody, or even later, on the Orca. (00:36:05)
Continuity mistake: Quint embeds his machete into the wood at the side of the boat, but in the following wideshot the machete is gone. Then as Orca starts to move, when Hooper says, "He's chasing us, I don't believe it," the machete is back. But when the shark leaps onto the boat the machete is gone again, and then as the shark devours Quint the machete is back for him to grab, so he can valiantly stab the shark. (01:44:30)
Visible crew/equipment: When the fishermen start out on the hunt, Ben Gardner appears in a close-up leaning on the windshield at forward deck, while talking to his boatmate about how stupid some of the others are. In the next wide shot of the boats, Ben's green boat is towards the left of the screen, and the large reflector screen and camera, that are mounted to the bow of his boat, are visible in front of the forward window where Ben was seen in the previous shot. (00:30:25)
Continuity mistake: When Hooper gets his gear from below, after the explosion in the engine room, he runs to the deck passing Quint using the fire extinguisher. The camera pans from Brody, who stands on the bridge deck, to Hooper right below him. So where exactly is the tall iron ladder that leads up to the bridge deck in this shot? It should be behind Hooper, in front of the window, but it's gone. Don't fret, it's back in the following shots. (01:49:05)
Continuity mistake: At the scene just after the fake shark scare, the real shark shows up at the pond area of the beach. As the lifeguard in a small boat reacts to everyone's panic, the shark tips over the boat then appears underneath him to tear his leg off. We watch as it sinks slowly to the bottom. You can plainly see that the lifeguard is barefoot in the boat. The severed leg has a tennis shoe on. (01:02:15)
Continuity mistake: Orca's ID number normally reads MS 15 LF on both her port and starboard side at the bow. However, after Quint shouts, "Hooper, you idiot. Ain't you watchin it?" Orca's ID number reads M 15 L at starboard side and 15 LF at port. (01:16:30)
Revealing mistake: While Quint is in the shark's mouth, the comfy white cushion is visible under his back, protruding from the shark's mouth. (01:57:30)
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)
Continuity mistake: The number of barrels on the deck of the Orca changes from shot to shot, during the final scenes at sea. (01:41:00)
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)
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: When Quint goes below deck to get the machete, with the intent to cut the barrel lines, the machete he takes is shiny and clean, with no rust or pit marks at all. Yet, when Quint holds it over his head and then embeds it into the side of the boat, the entire blade is rusty and full of pit marks. (01:44:40)
Continuity mistake: When Brody is throwing chum in water and Quint is in the chair they show him wearing no socks and old tennis shoes. After Brody falls and then sets a new chum marker Quint has brown socks on and loafer type shoes. (01:12:45 - 01:14:00)
Continuity mistake: Quint slams the machete into the wood beside the side cleat, and rigging lines. However, when the shark joins them aboard the boat and Quint is sliding towards its mouth, the machete's position changes - it is farther down towards the stern, note the black anti-slip mats. (01:44:30 - 01:57:00)
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)
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 the close-up of the stern cleat as the shark pulls on the line, there are two large metal 'L' shape brackets screwed onto the corner of the wood of transom. Amazingly, these large brackets are not screwed into the wood in the close-up, as Brody winds the line round the cleat just a moment earlier. The metal brackets repeatedly appear and disappear. (01:42:30)
Revealing mistake: While Hooper is below in the cage, he sees the shark nearing and up on deck as the barrels speed closer, the black triangular device attached to their lines is clearly visible, right in front of the barrels. The device pulls the barrels, not the shark. (01:53:15)
Continuity mistake: Quint remarks, "Back home we got a taxidermy man. He gonna have a heart attack when he see what I brung him." In the shot of Orca's stern, just prior to this comment, the two attached yellow barrels are very worn, with many black marks all over. Yet, in the shot right after, both yellow barrels are almost entirely yellow - quick paint job. Throughout the Orca scenes the marks on all the barrels change many times in consecutive shots. (01:43:20)
Continuity mistake: During numerous close-ups on the bridge deck, such as when Brody is behind the wheel, as Hooper shouts, "Our injectors got scored from the salt water in the fuel," the three large gauges over the steering column are seen. The center gauge has a wide shiny chrome trim, and a partial black face with a silver center. However, in the extreme close-up of the gauge panel, it is an entirely different style RPM gauge, and it now has a blackish rusty trim, and a solid black face. (01:41:00)
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.