Continuity mistake: When Quinlan is with Joe Grandi at the bar, Quinlan breaks his sobriety while seated at a round table, but in the last overhead shot the table is rectangular. (00:57:00 - 00:58:25)
Visible crew/equipment: Spade returns to Brigid O'Shaughnessy's apartment and tells her about his meeting with Joel Cairo. Right when he says, "He offered me $5,000 for the black bird," the shadow of the boom mike can be seen above the fireplace. (00:31:55)
Visible crew/equipment: Lightning equipment is reflected in Norma Desmond's glasses when she is drying Gillis by the pool. (00:55:30)
Continuity mistake: After Elsie has been kidnapped, there is a scene where a little girl walks up to an old man to ask him for the time. A man notices this and walks towards the old man. The old man is standing in front of a light pole which casts a shadow onto the pavement. In another shot, there are no shadows near the light pole.
Continuity mistake: Devlin walks in Huberman's place, and she is lying on the couch with a glass of milk right in front of her eyes. The angle of the camera is skewed to show her POV, but the glass of milk has vanished.
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)