At Freddie's apartment, the back of John's suit coat is covered with soot from his fireplace. But when he returns home after punching Freddie in the nose, the back of his suit coat is clean.
When John Hill is trying to open the davenport that is supposed to fold out into a bed, it keeps closing on him, to comic effect. When he tries to spread a sheet over the mattress, the wire extending from the back of the davenport to the front edge that keeps pulling it closed is visible.