Continuity mistake: Doc Riedenschneider calls on Cobby in a dark hallway with brick walls and a door in the end with a half-open transom. Through this door, in the adjacent room, there are several gangsters seated a table. They go down the hallway and enter this room. In the next scene they have entered and the seated gangsters are suddenly no longer there. Nor is there a transom over the door. The hallway viewed from this room has white walls now instead of brick.
Visible crew/equipment: When Joe Gillis returns to the mansion, after Betty Schaefer has just revealed her love towards him, when he enters his room, you can see a hand wearing a watch in the mirror. (01:26:50)
Visible crew/equipment: When Fabian goes into his office after receiving the package, he closes the door and the rest of this shot is through the glass. The camera and its operator (with a white shirt) are visible on the right side.
Continuity mistake: Dr. Luther Brooks is in the changing room with Dr. Dan Wharton. During their conversation, one of the lockers behind Brooks' is open, its door quite close to him. In the close-ups though, all the lockers are closed. The shadows are also different. (00:04:00 - 00:04:40)