In the three film generally rolled around by film historians as the 'first Film Noir,' M, Stranger on the Third Floor and The Maltese Falcon, Peter Lorre stars in all three.
on the rainy night when Ward and Jane for the first time go to the room he's renting we may notice different water stains on his coat in consequent shots. The left sleeve is dry before they enter the room, once they get inside coat's sleeves are wet.
When Jane leaves the coffee shop to follow the Stranger, the shades on the doors are shown to be higher from the outside than they were from the inside.