Continuity mistake: In one scene, Elvis Presley's prison uniform displays the number 6239, yet in another it becomes 6240.
Continuity mistake: At one point, the gigantic title character knocks over a city bus. For a moment, the word TONKA can be seen on the underside of the vehicle.
Visible crew/equipment: During the "How Long Has This Been Going On" number, Hepburn dances by a mirror - reflected in it are the camera crew, desperately trying to get out of the image.
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.
Other mistake: When Kirk Douglas 'appears' to pull a knife from his collar and throw it into Lee Van Cleef's chest, you can see Kirk pick the knife up from a trough in the front edge of the bar. The knife is already in his hand when he reaches to pull the knife from his collar.
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.
Continuity mistake: When Katharine Hepburn carries the white carnations out of the elevator (which have just been given to her by Gig Young), they turn pink when she steps off the elevator and walks outside.
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.
Continuity mistake: When Fred Astaire and Cyd Charisse are dancing among the parallel bars, her skirt changes to cullottes then back again to an ordinary skirt.
Continuity mistake: When the group go out to inspect the house damaged by the monoliths, the dirt around the rocks is white while the rest is dark. The professor squats down and picks up white dirt in his left hand and dark dirt in his right hand, then calls the geologist. In a close up, he opens his hands and the dirt colors have changed hands - the shot has been reversed.
Factual error: In the film the scientists are discussing the growth rate at which Lt. Col. Glenn Manning is experiencing. The scientists explain that the heart is made up of just one cell, but this is not correct.
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.
Plot hole: If Ashley kisses somebody, her good luck is passed on to them. However, Ashley kisses Chris Hemmington before she kisses Jake, so shouldn't Chris Hemmington have her luck?
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: During the slow-motion sequence, Speedy slams the mallet on the cat's paw and leaves the mallet on the ground when he rescues the mouse. When he puts a stick of dynamite on the cat's tongue, the mallet has gone.