Shortly before the end, the bedside telephone is shown in closeup, and the paint is chipped in several places. However, at the end, the telephone is pristine.
Twice, Leona turns on a radio, and music begins instantly and strongly. Radios of the film's era contained vacuum tubes that needed some time to warm up.
After Leona calls the police, she reaches for medicine and water on her bedside table. The table extending over her bed immediately at her right hand, and the phone is on the bed at her left. In the next shot, the phone has moved, and the bed table is far away from her, under the window to her left. However, in that scene the audience sees a reflection of the scene in a large mirror, so it's only a illusion that the telephone "moves" to the other side of her.
Henry Stevenson is driving Waldo Evans home in his car on a rainy night. At the end of the car ride, Waldo tells him to stop at number 54. Towards the end of the film, when Waldo calls Mrs. Stevenson to tip her off to her husband's misdeeds, he says that he is now at his Manhattan address but will be leaving after midnight. His address number is visible over the glass window over his head, and the actual number is 26 (read backwards). It could be the apartment number inside a building at 54, but the street name is never given.
[See "Error in Geography" GOOF beginning "Another observer states ..." for explanation.]
Whenever the camera pans out Leona's window to the cityscape with moving cars, city lights, etc., the smoke coming from smokestacks never moves.
When Fred Lord tears out the newspaper clipping about Henry, he rips with gusto, yet the tear manages to go straight and makes right angles, resulting in a perfect extraction of the news item. The paper must have been perforated.
When the doctor is talking to Henry about Leona's condition, the clock on his desk advances almost ten minutes; they actually talk for no longer than three minutes.
Through the open window in Leona's bedroom, frequent trains are visible crossing Queensboro Bridge, and the existence of these trains is important because on the phone, the murderer tells a pal that he will wait until a train is crossing "in case her window is open and she should scream". The trains were a branch of the Second Avenue Elevated that crossed to Queens, but that service was discontinued in 1942. The action could have taken place before 1942, but the Chrysler convertible in which Henry gives Waldo Evans a lift is a 1946 model at the earliest. The movie was made in 1948, but the footage showing the trains on the bridge must be from an earlier filming.