Visible crew/equipment: When Bond tries to get the golden bullet from the belly dancer named Saheeda, some angry gangsters enter her dressing room. As they start destroying the place, you can see the crew in the mirror on the dressing table very clearly after one of the bad guys is knocked into it, nudging it out of position.
Revealing mistake: During the fight scene in the belly dancer's room, Bond spins the bald guy around to avoid being hit by a chair. When the bald guy gets hit in the back with the chair, you can see a large rectangle of padding under his jacket.
Continuity mistake: During the chase scene with the police, Bond swerves past a driver in a dark green 1956 Plymouth Savoy. As the police cars pass the Plymouth, the scene cuts to an inside shot of the car with the driver yelling, then the driver loses control of the car and rolls it over. The car that crashes is a green 1955 Chevrolet 210 series, not the 1956 Plymouth.
Revealing mistake: In the shot where Bond rams the long tail boat of the karate experts, you can see that the boat is split in two pieces and the bow is already sinking before the collision.
Revealing mistake: At the start of the film when the gangster lands on Scaramanga's island, and enters Scaramanga's fun house, he encounters a scene where some dummies of Al Capone and some other gangsters come out of an area guns blazing... With the first burst of machine gun fire, the dummy "blinks"...
Factual error: The film's car chase takes place in Thailand, where vehicles are right-hand-drive (RHD) and travel on the left side of the road (as in England and Australia). Yet the American Motors (AMC) cars in the chase (the red Hornet X, gold Matador coupe and several Matador sedan police cars, all 1974-models) are all left-hand-drive cars. Scaramanga's car can be excused as something he specifically imported for himself, but the Hornet is 'borrowed' from a fictitious AMC dealership (none existed outside the USA) and the small amount of AMC vehicles sold outside the USA were shipped disassembled to various companies that reassembled them and sold them under their own company names (AMI in Australia, Karmann in Germany, etc). Companies such as these, in RHD nations, had to modify the cars to RHD themselves in order to be allowed to sell them 'locally'. So the Hornet would have been at a non-AMC dealership, and would have been RHD, as would the fleet of police cars. Naturally, this 'error' was created by AMC's promotional deal with the filmmakers to use AMC cars in order to improve US sales to the US filmgoers.
Deliberate mistake: In the scene inside the belly dancer's dressing room, during the brawl Bond has with the KGB agents, he shoves the bald headed guy into the mirror along the bottom 1/3rd of the glass, yet the middle along the left hand side of the mirror makes it look as if that was the initial point of impact before it shatters.
Audio problem: In the teaser we see the hitman load his gun when he gets ready to kill Scaramanga. When Scaramanga walks into the room, the hitman aims for him. The gun makes a loading sound. Upon the hitman's arrival to the room he racks a bullet into the chamber therefore no other action would be required to make the gun ready to fire. A loaded gun does not make a sound when you aim it - and why would he have unloaded the gun while waiting for his victim? When you load the gun, the hammer is back and the gun is ready to fire. No further actions are necessary. And a professional hitman does not wait to turn off the safety on his gun until his victim has arrived.
Continuity mistake: The AMC Matador stops as the AMC Hornet X races by on the cross-street. As the Matador halts, we see it has a proper door mirror. In a close-up of Scaramanga driving, we can just see the hole in the door where the now-missing mirror was mounted (on the VHS full-frame, we can see the remote cable hanging from the hole and the base of the mirror swinging as the mirror hangs out of view).
Continuity mistake: When the AMC Matador arrives in the hangar and begins attaching the jet plane equipment, we see a bracket welded to the lower rear quarter panel, just behind the door. The wing supports swing down to attach at this point on both sides of the car, yet these brackets were not on the car in any prior shot.