No tape in the tape recorder when Superman/Kent starts "play" to hear Jimmy.
Jimmy falls through a trap door in the floor that's constructed from two rectangular pieces of wood that swing open in the center and the person standing on it falls down. Later when Superman rescues him he rips the trap door off from the floor but when he does it's one big square piece not two smaller rectangular ones like before.
Homer Garrity shows Jimmy the one way window, but when Jimmy later opens the door, the supposed-mirror side is clear.
Just after the henchmen leave the room where they have dropped poisonous gas pellets you can see the head of a crew member in the bottom left hand corner of the screen.