Revealing mistake: James Bond and his two friends are hiding underwater while Dr. No's thugs search the river with dogs. Bond had very quickly cut three hollow bamboo stalks to use to breathe underwater through the stalks. However, you can see the sections in the bamboo, so the closed stalk sections, separated by the natural divider, would not allow air to pass through. Bond hadn't cleared through the sections with a thin pole, so these would not have been usable as breathing tubes without more work. (01:10:00 - 01:12:00)
Revealing mistake: When Bond and Honey are made to take showers to clean them of any remaining radioactivity, they are meant to be naked. When Honey gets out of the shower a man holds a towel up for her, but if you look closely you can see that she is wearing a flesh-colored swim suit. (01:16:45)
Revealing mistake: Every time a shot of the hallway outside of Bond and Honey's room in Dr. No's lair is shown there are several doors on the same side of the hallway that lead too nowhere. Notice when Bond enters the room looking for Honey near the end we don't see the reverse of the doors from the inside of his room.
Revealing mistake: When Bond fights Quarrel and Pussfeller at the back of restaurant we can see that Pussfeller is replaced by a stunt double. (00:28:50)
Revealing mistake: After Bond attaches the silencer to his gun, the next shot is of Professor Dent approaching the house at nighttime. However, this shot is the same shot from earlier of Bond approaching the house during the day. It has simply been mirrored and darkened to hide this.
Revealing mistake: Bond, Quarrel, and Honey are supposed to be walking through a saltwater river and yet none of them seem to react when coming out of the water with their eyes open so obviously it's fresh water used in the river. (01:15:10)
Revealing mistake: The second car chase is made with the help from a greenscreen. The car's movements as seen on the background doesn't always correspond with Bond's steering and the following car is sometimes too close to the screen. (00:48:10)