Revealing mistake: When the defective shell is about to fall, the ground has no sand mounts. Couple shots later, now on the floor, the shell turns around following Chaplin. Watch and you'll see that a sand mount has magically appeared close to the shell to hide the white mechanism that makes the bullet turn.
The Great Dictator (1940)
1 revealing mistake - chronological order
Directed by: Charles Chaplin
Starring: Charles Chaplin, Paulette Goddard, Henry Daniell, Jack Oakie, Reginald Gardiner
Continuity mistake: When Hynkel is removing Garbitsch's medals, a medal with a cross, close to the left armpit, disappears without Hynkel having touched it.
Adenoid Hynkel: Garbitsch, what's the meaning of this? These appropriations? Twenty-five million for prison camps when we need every penny for the manufacturing of ammunition's?
Garbitsch: We've had to make a few arrests.
Adenoid Hynkel: A few? How many?
Garbitsch: Nothing astronomical. Five or ten thousand.
Adenoid Hynkel: Oh.
Garbitsch: A day.
Adenoid Hynkel: A day?
Garbitsch: Just a few dissenters, that's all.