Gilda (1946)

Revealing mistake: When Ballin's plane flies and finally crashes, it becomes obvious that the horizon is a still image with the film of the explosion superimposed directly onto it.

Sacha

Gilda: Got a light?
Uncle Pio: Yes, Mrs. Mundson. It is so crowded and yet so lonely, isn't it?
Gilda: How did you know?
Uncle Pio: You smoke too much. I've noticed. Only frustrated people smoke too much and only lonely people are frustrated.