Revealing mistake: The secretary turns on the tape recorder to play back her employer's dictation. His voice starts speaking, but the tape reels aren't turning, and the button she pushed hasn't stayed depressed. Apparently, the machine isn't even on. (00:01:20)
Too Many Christmas Trees - S4-E13
Continuity mistake: When Steed and Emma are driving to the estate, the car's windscreen keeps disappearing. It's there in full shots, gone in close-ups, and reappears again every time we cut back to a long shot. (00:10:30)