Revealing mistake: When Bond and Che (the big black guy) are fighting, Che lands on a rug behind Bond. As he gets up again one can see a brown mat underneath the rug. It's very noticeable by the way it moves as Che pushes himself up. (00:13:55)
Revealing mistake: When the white race car with the number 6 is turned over there is a closeup shot of the driver obviously hanging head down in his seat. If you look closer you can see the spectators in the background also upside down. (01:47:20)
Revealing mistake: While the lab explodes, Blofeld jumps a ditch followed by Bond. Bond's stunt is noticeable because of his longer and light brown coloured hair, as opposed to Bond's very dark colour. (02:11:40)
Revealing mistake: When Bond throws a Blofeld henchman off a cliff near Piz Gloria in the Alps, you can see that it is a dummy, as its arm swings round and wraps around the whole dummy.
Revealing mistake: When Bond slides along the ice he is very obviously grabbing a cable that pulls him along.
Revealing mistake: When Blofeld escapes from the Lab, Telly Savalas is replaced by an obvious stunt wearing a bald cap that protrudes around the forehead.
Revealing mistake: When the thug is stuck to the spikes on the wall, the protruding safety pad under his clothes is very noticeable.
Revealing mistake: When Irma Bunt is firing shots from her gun in Blofeld's car towards the end of the movie, Blofeld is a dummy and not Telly Savalas.
Revealing mistake: At the end, when Bond is chasing Blofeld, there is a shot of him hanging onto the edge of a cliff. There is a bit of snow moving up towards him, meaning that this shot is played backwards.
Answer: It's an entirely intentional aside to the audience, the one occasion in the entire Bond series where the so-called 'fourth wall' (i.e. the cinema screen itself) is broken. As such, within the context of the film itself, it doesn't really have much of a meaning.
Tailkinker ★