The Roaring Twenties (1939)

Revealing mistake: When a car drives by a store front and two hand grenades are thrown at it, the hand grenades bounce back into the street before the store blows up.

Eddie Bartlett: One thing, Lloyd. They tell me your boss is building a case against our old friend, George.
Lloyd Hart: The case is already built, Eddie.
Eddie Bartlett: Yeah, well, you remember what he said would happen if you ever told what you knew about him?
Lloyd Hart: I remember.
Eddie Bartlett: So does he.