Continuity mistake: In one scene, Elvis Presley's prison uniform displays the number 6239, yet in another it becomes 6240.
Factual error: When William Holden visits the Special Operations HQ for the first time a black vehicle is seen pulling in to the complex. The car is a 1948 Dodge or other Chrysler product which had not yet been manufactured.
Continuity mistake: When Chaplin is inside the elevator, the hose changes from being tied knee level to hip level, depending on the shot.
Deliberate mistake: At the beginning of the movie Mr. Coates tells his wife that he will be gone "all of three months, maybe four." The first time we see Bud and Elizabeth Searcy she tells Travis that her dog is pregnant and that Old Yeller is the father. We then see her dog that does not look very pregnant. The next time we see Elizabeth she presents Travis with one of the pups. The problem is that the pup that was supposedly just born is about 4 months old.
Factual error: In the last scene of the chess game, you can see that both the Knight and Death have castled. Castling was introduced to the game of chess in the 16th century, well after the film is set.
Other mistake: When Cary Grant came to visit Deborah Kerr, he laid his coat and hat in the chair. Later he remembered he had a gift from his grandmother for her. He did not have it when he came in. Someone had to put it under his coat.
Revealing mistake: Allison is wounded by a grenade fragment while disabling the Japanese 105's. But when his bloody shoulder is first seen, the blood stain is visibly too bright for real blood.
Character mistake: About half-way into the movie the Captain asks for a fathometer reading and is told 150 fathoms. He preforms a mental calculation and says that it is 310 meters and over a thousand feet. In fact, 150 fathoms is 275 meters or 900 feet (1 fathom = 6 feet = 1.83 meters). (00:57:15 - 00:57:40)
Continuity mistake: At the start of the film when Tom is doing his trial run, he is forced off the road to avoid crashing into two oncoming trucks, driven by Johnny and Red. His truck has the number thirteen number board on the front, which isn't on it during any other time during the trial run, although it's on the truck for the rest of the film.
Deliberate mistake: When Henry Fonda decides to recreate the old witness' ability to get to the door in 15 seconds, he asks another juror to time his walk. The scene never cuts away, but the juror who times it says it took 41 seconds when in reality it takes exactly 31 seconds, you can time it.
Factual error: As the movie opens, the submarine is dispatching frogmen to acquire Japanese mines that are sonar-proof. The problem with this is that in order to locate mines by sonar, either the mines must make noises to be picked up by passive hydrophones, or the submarine has to start pinging with active sonar. Doing this makes the submarine vulnerable to any enemy listening in. I can't imagine a submarine venturing into a mined strait, announcing to one and all, "Here I am"..
Continuity mistake: In the scene where Glen Ford shoots the stagecoach driver dead, the body falls to the ground. Glen Ford gives the order to put the "dead" man on the saddle of a horse. When the men lift him up, the "dead" man puts his right hand up onto the shoulder of one of the men.
Factual error: While flying across the U.S. before the Atlantic attempt Stewart lands and exits the plane. While doing a quick inspection of the airframe he approaches the engine and puts his hand on one of the radial engines cylinders which would have still been several hundred degrees, so should have resulted in a serious burn.
Continuity mistake: According to one of the characters, the firing squad is drawn from the 3rd Battalion of the 701st Infantry Regiment, the same regiment as most of the other characters. However, all the members of the firing squad (except the officer and sergeant, who are credited characters seen elsewhere in the film) have "710" on their collar patches. This can be seen when the sergeant, who has "701" on his collar patches, is briefing them.
Audio problem: The Sergeant is calling "Sunrise 6" on his radio hand mic, then tucks away the mic to scan the mountain with binoculars, but his voice is still calling Sunrise 6.
Continuity mistake: The Sergeant (played by Karl Malden) is on leave with his family when the car needs water. His daughter (played by Natalie Wood) gets out and refills the water. During the conversation, Malden is bare headed, then immediately after he has a hat on.
Continuity mistake: The character Sid Sorokin sings the song "Hey There" into a dictograph machine. He then plays it back and sings a "duet" with himself. However, the lyrics and melody at the end of the song are different from what he sang into the machine originally.