Errors made by characters (possibly deliberate errors by the filmmakers): The name of the flower shop owner is Gravis Mushnik, but the shop sign says "Mushnick's".
Continuity: Frank walks into Detective Fink's office, sits down and lights a cigarette. The cigarette remains in his mouth until a close-up shot, where it is missing. When the wide shot is resumed, the cigarette is back again.
Continuity: When Winifred begins sipping her Dr. Slurp's high-octane 'cough medicine' in the bedroom, the bottle is almost full; a moment later when she walks into the living room, the bottle is half empty even though she doesn't drink again until Seymour is leaving.