When Albert Sully pins an explosive device on his enemy's coat lapel, the close-up of the action uses a different coat and tie than the one worn by the character in the wide shot.
Napoleon Solo drops an explosive device into a sealed container for "safe" detonation. But a wisp of smoke escapes from below the rim on the side of the container before he opens the lid to release the intended cloud of smoke, revealing that the container is just a prop.
The London taxi has a left hand drive like an American car, unlike the right hand drive cars used in Britain.
When the Baroness first meets the group in the nightclub, Sully asks her to not speak in, "that Flemish patois." But she was speaking with a French accent and Flemish is Dutch, which wouldn't make sense.