Continuity mistake: In the scene where Ursula Andress confronts Marcello Mastroianni, he reaches into an ice bucket where you see a very small pistol (PPK). When he points it at her, it changes into (I think) a Colt 45. It then, in another angle changes again into (I think) a Mauser Parabellum... Mistakes can be made if filming covers many days on the same scene, but when the dialogue mentions how he can hide a tiny pistol in the ice bucket.....
Factual error: Terry-Thomas's plane gets stuck between the carriages of a Paris-bound train (in fact filmed on the single-line track between Bedford and Hitchin). Just before the train plus plane goes into a tunnel you can see the cooling towers of Bedford's Goldington Power Station (circa 1960) behind TT's head. (01:58:20)
Audio problem: In the scene when Carole catches Ms. Lefavre in Michael's apartment, she (Ms. Lefavre) tries to cover by pretending to be Michael's maid. As she moves about, cleaning various items, she talks about all the work she has to do, etc., etc. However, throughout this entire sequence her mouth never moves or so much as opens.
Continuity mistake: In the film the Eye Creatures have landed their spaceship in a field during the night and the Army has been called in to survey the spaceship. A soldier gets on top of the space ship and starts using a welding unit to try and open it and it's bright and clear out. The temperature of the welding ignites a fuse on the spaceship which causes the ship to explode. When the scene shows the spaceship blowing up it's now pitch black outside.
Continuity mistake: In the scene where Rusty is trying to keep Dana and Valerie from seeing each other, it is supposed to be night time. But, when Rusty opens to curtains to usher Valerie out the door, you can see that the sky is much too light to be night time.
Continuity mistake: During Janet's musical performance in the French cafe, she is wearing cymbals on her knees in one scene; in the next, they are missing.
Revealing mistake: In the scene at the end of the movie where Lee Marvin is running interference during the escape by shooting in the air, horses pulling a beer wagon get startled and run into the street where the wagon turns over.At the beginning of the shot, when the horses begin to bolt, you can see the stuntman driving the wagon. He is sitting low behind the wooden front of the wagon (which has holes cut in it so he can see out).
Continuity mistake: When the crooks are climbing over the wall into the police station yard, when they are on the pavement, the ladder dosen't reach the top of the wall. But when seen from inside the police station yard, it reaches above the wall and looks like a different ladder.
Character mistake: On a pillar in the department store, there is a sign saying "Bear, Tiger, Zebr Skins." It should read "Zebra."
Other mistake: FBI Agent Kelso believes a cat may be able to lead him to the location of a kidnapped bank teller. He has four other men trying to follow the cat. When Agent Cahill reports that he is stationed "west of Whittier Street," Kelso sticks an identifying pin on a large map but he puts the pin in a location east of Whittier Street.