When Scott returns to Las Vegas to reconcile with Mary, after their kiss is interrupted by whistling, both of them have noticeably different hair arrangements than when they started kissing.
Scott walks into the back room of a casino where William and Sacramento are playing poker and speaks to them. During this period Sacramento is wearing a hat. The camera follows Scott when he leaves the room but when it returns to the game Sacramento is now wearing an eye shade.
When getting into a fight with a love rival, Robert Young throws what may be the least convincing punch in film history. He misses by a country mile.
After Mary punches Scott in the nose, just after he walks off, a clear shadow of the boom microphone is visible moving on then off the patio umbrella by Mary's head.