Lily unscrews both light bulbs in the hallway outside Roy's apartment. In a following cut, Roy is seen entering his apartment from a well-lit hallway.
When Lilly shoots Myra, the gun makes a huge bang, but when she got it out before, she had screwed the silencer onto it.
In the train, when Roy is grifting the sailors, you can see
that he is only rolling one die at a time. However, you can distinctly hear him drop two dice (out of the frame) to the table at the end of the game.
At the end of the movie when Lilly is leaving Roy's apartment with his money, blood is clearly visible on her knees and calves. But moments later when she is going down in the elevator, her legs are clean.
At the end of the movie, when Lilly picks up the briefcase full of money to flee Roy's hotel room, several bills can be seen sticking out of the briefcase. However, in a previous shot, where she closed the briefcase and set it on the floor, these bills were not visible.
When Roy visits Lilly in her hotel room to repay his medical expenses, there is a boom mic clearly visible.