Continuity mistake: Ethan and Grace are in a car chase, trying to get away from Paris. The Fiat Ethan and Grace are driving makes a left turn, and you see a dark blue car parked at the corner. Paris is driving the armored vehicle and makes the same turn, but the dark blue car has disappeared. (01:07:36)
Continuity mistake: During the Venice scenes, Ethan's hair length is always the same, except for scene number 1 where he and the team are on a boat arriving in Venice, and scene number 3 where he and Ilsa are on a balcony. In both these scenes, his hair is very short.
Continuity mistake: When the submarine is hit, the centre is blown into a million pieces. In the next shot, the submarine floats gently to the sea floor untouched. Then it semi-crumbles as it lands.
Continuity mistake: When Grace crashes with the Italian police car, the door is opening up on the top because it was dented. When she puts it in reverse, the door is back in a normal state.
Continuity mistake: On the roof of the train, Hunt is on top of Gabriel, with a blade right next to his neck. Gabriel says "I know what the key opens," and right then the blade is either touching his skin or inches away, depending on the shot.
Continuity mistake: In the desert, when Ilsa is shooting with her eye patch on, a strand of hair on her forehead suddenly disappears between shots.
Answer: Maybe they didn't have any guns at that point.