Continuity mistake: Chief Brody has a cigarette dangling from his lips as he famously tells Quint, "You're gonna need a bigger boat." In the overhead shot as the shark passes the stern, just below Quint, Brody flicks his cigarette towards the left of the screen. However, when Hooper leaps down the ladder Brody's cigarette is back in his mouth. (01:21:20)
Continuity mistake: In one of Richard Dreyfus' first scenes, Brody asks him to help with the group of men crowding into a small boat. Hooper says that the officer wants him to tell them that they're overcrowding the boat. They show the men climbing in and there's a guy in a blue jacket climbing down the ladder into the boat. He waves his arm and says "what do you care?" They then show Hooper asking if they know a good restaurant or hotel on the island. When they show the men again, uttering the line "Yeah, walk straight ahead," the man in the blue jacket is on the deck again and is again descending down the ladder. (00:29:00)
Visible crew/equipment: When the man is in front of Brody talking to him on the beach the film crew are reflected in Brody's glasses.
Continuity mistake: On the Fourth of July, Sean (the youngest Brody kid) is wearing a white t-shirt with orange around the collar, and green shorts. But after Michael goes into shock and Sean is seen crying, he's suddenly wearing darker shorts and a plain white shirt with no orange. Later at the hospital, he has his orange and white shirt and green shorts on again. (01:01:55)
Factual error: Shooting an oxygen tank (or even an air tank) would not cause it to explode, rather the tank would just empty quickly, but it wouldn't blow up, no matter where the bullet hit.
Factual error: When the woman is yelling that the shark is in the pond, it shows the shark's dorsal fin and tail fin sticking out of the water. The tail fin is moving straight. If the shark needs its tail to swim, wouldn't the tail fin be moving side to side? (01:01:00)
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)
Visible crew/equipment: After hoisting up the damaged cage, when Quint walks over to stand beside Brody in the close-up the reflection of a male crew member's head is visible in the window, behind the ladder, until Brody lets go of the line. The crew's moving shadow is also visible under the cabin window, just after Quint passes it. (01:56:40)
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)
Revealing mistake: While the shark's face is up close and personal in the cage with Hooper, the equipment under the shark is visible as the camera pans back and is visible again in following shots. In the shot just prior to Hooper swimming away the device is quite clear. (01:55:00)
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)
Revealing mistake: After Hooper delays Quint's shot of the very first harpoon into the shark, he finally shoots and hits the right side of the shark's dorsal fin. Problem is that in this particular shot there is another harpoon already on the left side of the shark's dorsal fin! This is the exact same shot seen later in the film, after Quint shouts, "Run him down Hooper!" (01:24:50 - 01:41:00)
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)
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.