After the robbery of the wealthy woman's home the paper says a maid was struck and seriously injured; and later in Cagney's office they're still talking about a maid who screams. Later when the guy who actually hit comes back scared; he's says the butler died.
When Cagney's character asks film reviewer "Mr. Blair" into the men's room at The Cocoanut Grove to "discuss" his latest review, all of the stall doors are closed. After Cagney forces him to eat his review, the third stall door is open (no one enters or exits the room during this scene).
When Dan first meets Lois in her dressing room they are briefly interrupted by George who hands Lois a magazine. He tells her that she is on the cover of the magazine called "Filmed Life." They use the real fan magazine Photoplay as a prop. The Photoplay title is clearly shown when Lois is looking at it.
Dan just gets released on bail and then is in the car chase and shoot-out at the end of it. Where did he get the gun he uses to shoot Spade?
When Dan's former gang approaches the car offering a tour of movie stars homes, they walk through the shadow of the boom microphone - which can initially be seen on the street at their feet, then it rolls up all four as they walk to the side of the car.