In the beginning, just after Dick Powell sits down in his office, Raymond Burr starts talking, but one part of his speech is an obvious cut with a different recording of his voice between two other cuts. ("Just a kind word, and a pat on the back for a job well done.")
When John goes to Mona's apartment, he walks up the stairs where, at the top, there is a window into her kitchen and the apartment door. However, in the next shot from inside her apartment, when John pushes her door open, the arrangement and alignment of the hallway and stairway has changed and the railing of the stairs is different.
When Macdonald is talking to Forbes about Mona and a new case, he is sitting down and leaning on the desk with his right elbow. On the following cut, he is then leaning back with a cigarette in his mouth and preparing to light it.
Mona calls John to warn him that Bill might be coming over to get him, and John turned out all of the lights downstairs. His son, Tommy, then comes downstairs to say good night to him. As Tommy comes down the stairs, the stairway itself is lighted and he casts a shadow on the wall. They bid each other "Good night," and Tommy goes back up the stairs. But when Tommy goes back up those same lighted stairs he now cast no shadow on the wall.
When Macdonald and Forbes are talking about the case in the beginning, MacDoanld is holding his hat. On the following cuts, his right hand changes orientation several times between his holding his hat and touching his face.
The public elevator indicator in the Los Angeles Hall of Justice building shows floors 1 to 19. However, in reality, the building is only 14 stories tall.
When Forbes enters Mona's building, he passes an apartment with the number 108. When he looks at the mailbox to get her apartment number, it turns out to be 112. The apartment numbers from 108 to 112 indicate five units; however, there were only four units as indicated by the amount of mailboxes.
At 16 minutes John & Mona go riding in her boat. The windscreen is low and Mona's hair is freely blowing in the breeze. John's hat should have blown off with that force of wind.
When Forbes arrives at Mona's building and looks at the mailbox to get her apartment number, there is an apartment next to the mailbox that reads #108. Forbes then had to walk up a flight of stairs, but when he reaches her apartment, it reads #112. Since her apartment was on the second floor, the number should have started with a "two".
After John shoots Smiley, the scene switches to Mona's apartment. MacDonald arrives, talks with Mona, then goes to make a telephone call. The camera switches over to Mona leaning against the wall. To her left is a framed photo of a quarterback with the ball in his upright hand preparing to throw (presumably Smiley?) sitting on a table or sideboard. As MacDonald can be heard dialing the phone, a shadow (of someone on the set) flickers on and off of the left side of the frame. It then returns and goes away even more noticeably than the first time.
When Tommy has a nightmare and his parents go into his room, a shadow of the boom microphone can be seen moving back and forth across the top of the wall in the room.