In the initial long-shot when McPherson and Lydecker are out to dinner, McPherson's chair is unoccupied (about 15:28). When the camera is at their table, McPherson has materialized.
When Lydecker is talking to Laura about Carpenter, he reaches for the file twice.
When Laura first tries to get Waldo to endorse a fountain pen, she holds the advertisement in front of her when they both are in the shot. When the shot changes to her alone, the advertisement has shrunk significantly in size. The advertisement resumes its original size moments later when both Laura and Waldo are in the shot together.
When McPherson first interviews Mrs. Treadwell, the position of his elbow changes between shots, from being up to resting on his leg.
When McPherson is seated talking to Carpenter at the country house, his position in relation to Carpenter changes between shots.
When Waldo retrieves the shotgun at a quarter-to-ten, the clock chimes the 45 minute signal, but never chimes the 9:00 o'clock hour.
When Lydecker slips back into Laura's apartment at the end, he retrieves the shotgun from the clock but shows no reaction that the empty shells have been removed. He should have shown worry on his face that the police had discovered the gun and are on to him.
Waldo does react, mildly; his eyebrows raise significantly after he opens the breech.
Waldo does react, mildly; his eyebrows raise significantly after he opens the breech.
Waldo Lydecker mentions that Lt. McPherson was wounded at the siege of Babylon, Long Island. An NYPD officer would not normally respond to calls for service in Long Island.
However, it's possible that McPherson come to the NYPD after serving in Long Island.
However, it's possible that McPherson come to the NYPD after serving in Long Island.
When Lydecker recognizes McPherson's name, one can see part of the waist-band of a bathing suit worn by Lydecker in the bath tub.
Throughout all of the action that takes place within Laura's spacious apartment, there are at least a dozen vases filled with fresh flowers. Considering the murder had occurred late Friday, and Waldo speaks of the heat on Sunday, at least some of the more delicate flowers should have wilted. But they are fresh as can be when Laura returns from the 'dead'.
When McPherson arrives to question Lydecker, he hears the fancy clock begin to chime. However, when he looks at the clock, it is seen that the hands have already advanced about two minutes.
When Lydecker gets out of his tub and puts on his robe, the seat of the robe is already wet, suggesting that this was not the first take of this scene.
The night of Laura's return, McPherson arrives at her address in a thunderstorm. As he relieves the other detective staking out the building, McPherson hands him a cigarette. The detective puts the cigarette in his mouth and walks out into the pouring rain.
The clock, which is heard to strike the time, only has one keyhole on its face. However, because the striking mechanism is separate from the timekeeping mechanism, a chiming clock must have at least two separate keyholes - one for the clock itself, and one for the strike. Presumably the prop was made only to keep the time since the production staff knew they would be adding the sound of the chime in post-production.
When McPherson and Lydecker are in the restaurant, Lydecker says he and Laura were at the same table on the night of her 22nd birthday. He then says they met 5 years earlier when she tried to hire him to endorse a pen for an advertising company where she worked. That would make her 17 years old and working in a professional position.
When McPherson goes to Lydecker's, he is nosing around with some of his art stuff and picks something up. Lydecker tells him to leave it alone or some such, as it is priceless and not to break it. However, it will be seen that Lydecker is in the bathtub, and the door is nearly completely shut; he could not have seen McPherson doing anything from that vantage.
Laura is considered a suspect in Diane's murder, although nobody ever explains how Laura could have known that Diane was in her apartment.
Laura is supposed to have listened to all of Waldo's records of his radio shows, yet she doesn't seem to know that his discussion of great lovers of history is a recorded rebroadcast.