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)
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)
Character mistake: When Brody waves at his wife Ellen she says "I've got Shawn." In the next shot he's running after his brother Michael going to the pond, so she has not got him at all.
Character mistake: Captain Quint tells Hooper and Brody that the USS Indianapolis delivered "the Hiroshima bomb" in 1945. This is a myth that has persisted for decades and right up to the present. To prevent it from being lost in one piece, the Hiroshima bomb was actually delivered in pieces by various means to Tinian Island, where the parts were reassembled before it was carried aboard the Enola Gay to its target in Japan. The USS Indianapolis delivered only the detonator for the bomb. (01:29:00)
Character mistake: When Hopper is in the cage you can tell it isn't him by the size of the scuba tank on his back and size of that kill stick he was going to use. The tank and kill stick are almost as tall as the person in the cage. When on deck and loading into cage in scene before that the items aren't that tall.
Character mistake: In the scene on the boat, when Quinn, Hooper and Brody are gathered below, Quinn gives the date about the USS Indianapolis sinking as June 29, 1945. It is actually July 29, 1945. The first atomic bomb wasn't actually detonated until July16, 1945 in Alamogordo, New Mexico making it impossible for the Indianapolis to be delivering the bomb in June.
Character mistake: At the beginning, Sheriff Brody walks onto the "boat" that takes people and, at most, two cars across the water to the mainland. A car joins Brody with 3 men, the medical examiner, the major and the newspaper man. Brody has been told, by the medical examiner, that it was a shark attack that killed the young woman who swam at night (the first death in the film) but now he is being coerced into saying it was a boating accident. Meanwhile, the man who handles the "boat" has already put it in reverse, heading back where they have come from Nonetheless, the mayor says, "You can take us back now." Turning around, he would have seen the folly in his words.
Character mistake: Chief Brody and Hooper go to the wharf to dissect a large tiger shark and examine the contents of its stomach. Finding nothing unusual, Hooper recommends they go offshore that night to search for the real killer shark because "he's a night feeder." Coming from a marine biologist, that remark really makes no sense. Hooper knew that, in addition to eating Chrissie the midnight swimmer, the shark also ate Pippin (the black Labrador retriever) and the Kintner boy in the middle of the day at a public beach. Based on all available evidence, the shark was no more likely to feed at night than in broad daylight.