Revealing mistake: In the scene where Bond is trapped in Largo's shark-infested pool, he uses his mini air tank to breathe. In most of the subsequent shots, look closely at the actor's face - it looks a lot more like a stuntman than Sean Connery. (01:20:20)
Revealing mistake: After Manco beats up Cavanaugh and places Cavanaugh's back up against the bar, while Manco faces him, three of Cavanaugh's henchmen appear at the entrance of the bar demanding that Cavanaugh be released. Manco turns around and kills all of them with his pistol, while Cavanaugh falls to the floor crawling toward his gun. Manco is walking toward the entrance of the saloon with his back to Cavanaugh. Manco draws his gun and kills Cavanaugh without looking at him. If you look closely at the tip end of the pistol, you can see that the only thing that Manco would have killed was the saloon floor. (00:17:00)
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.....
Continuity mistake: Harry Palmer uses the leather wrist restraints to lacerate his wrists - the pain enables him to resist being involuntarily hypnotised. The next time he is woken roughly by the guards for another hypnosis session, his wrists are unmarked.
Continuity mistake: Lombard trips going up the stairs in the dark; he falls on his right side, but he waves the others to go up lying on the opposite side, facing the opposite way. (01:04:30)
Continuity mistake: James Garner figures out he's being duped, and tells Eva Marie Saint to run out of the room screaming to draw attention to herself. She does and there's a shot of her on the hospital lawn with staff all around her. The next shot is James Garner looking out the window to see what their reaction is, and Eva Marie Saint can be seen behind him in the room.
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.