The Chrysler convertible has what looks like California plates (MLK 050) when Joan Molner first drives the car, but as she is approaching her destination, it has New York plates (7C 5976).
When Joan is being chased into the subway tube, black greasy stains are visible on the right breast of her white dress, then completely disappear seconds later.
The Imperial driven by Paul Hoplin changes from an old-style two-headlight model to the newer four-headlight version. Early, when Hoplin is in the phone booth, the two-headlight car can be seen in the background. Later, when he is driving Joan Molner to Vince's apartment, it is the newer four-headlight model. In 1957 the four-headlight system was optional, because it was not yet legal in all states. It became standard with the 1958 models.
When Joan is walking through the bank lobby, she is carrying the box with the striped top outward. In the next shot when she gets outside on the street, the bottom of the box is facing away from her.
When Joan exits the bank, the camera pans up to a building with large corner windows, and the blinds are down. But in the next shot, Paul is looking down from a corner window and the blind is up.
The $500,000 would equal 25,000 $20 bills and would weigh about 55 pounds. In bulk, it would be the equivalent of 11 reams of 20# copy paper. It would be too large to fit into the flimsy dress box and Joan could not carry it so easily.
During the subway chase, the lighting moves with the actors.
When Joan Molner (Inger Stevens) spoke with Agent Kole (Kenneth Tobey), she stated that she only knew the first name 'Paul' of the man holding her husband and daughter hostage. However, after getting the money, her thought narration stated the last name 'Hoplin' twice as she was trying to meet the 1:30 deadline.
Paul Hoplin introduced himself to Joan Molner by his full name when he arrived at the Molner residence to blackmail the couple. This made no sense, as he planned to have Joan Molner pick up the $500,000 from the FBI and she could have provided his name to the lawmen. Even if Holpin had not stated his full name, Joan's husband knew it and could have told her what it was. Fortunately, all Joan recalled in her encounter with the was Holpin's first name.
The little girl gets hysterical when the mother screams into the phone while talking to her husband. The husband didn't react in anyway before the little girl became hysterical so it was impossible for her to know her mother screamed since she could not have heard her mother.