The case
The 1979 Bond film gives the steel-toothed henchman a love interest, a small blonde woman in glasses and pigtails. Nearly everyone who saw it remembers the punchline: she grins and reveals braces to match his teeth.
The scene has been checked frame by frame. Her teeth are ordinary. The matching-metal joke is so good that memory wrote it in, and generations have described a shot that doesn't exist.
Why our brains do this
The setup practically demands the punchline, and memory supplies the joke the film seems to promise.
Sources: Wikipedia — Moonraker (film) · Wikipedia — False memory: the Mandela effect
