Revealing mistake: In the pilot episode (?). When old man Barnabas bends over Maggie's bedside to bite her, the strings holding his bald wig in place are visible, including the stubble, and wave of fake black wig hair. (01:19:29)
Revealing mistake: 1967: Barnabas and Vicky are talking in Collinwood's foyer when a great deal of noise starts interrupting the scene from backstage. You can hear coughing, several bumps and crashes, shouts, and finally, a fire extinguisher going off. Meanwhile, the distracted actors are completely blowing all their lines - but the unstoppable taping goes on.
Revealing mistake: 1968: When the psychic enters Quentin's haunted room, she stumbles over the wire used to "ghostly" open the door, and has to grab onto the gramophone table to keep from falling. The table almost falls over with her, but she manages to stay upright, barely.
Revealing mistake: 1966: Elizabeth is thwarted by a set door that refuses to open when she tries to make her exit. She struggles with it, tugging several times, but winds up just standing there, exasperated, until the scene ends a few merciful seconds later.
Revealing mistake: When "Dark Shadows" did its version of "Dr. Jekyll & Mr. Hyde," the Hyde character, John Yaeger, had prosthetic nose trouble during a fight scene. His rubber schnoz came unglued and nearly fell off. He was subsequently given a nose job.
Revealing mistake: 1967: The apparently miscued Burke enters the foyer set through a door and starts across the stair landing. You can then hear the director say, "Try it again," and he turns, goes back out the door and comes in again.
Revealing mistake: 1967, episode 86: Roger is late for a meeting because actor Louis Edmonds, forgetting he had another scene, had gone to his dressing room and undressed. Because it was "live tape," the other actors had to awkwardly ad lib until Edmonds could throw on a shirt and be hustled onto the set, whereupon one camera zoomed in tight on him and stays there for his solo shot making a toast. You can hear the stress in the other actors' voices as they stifle laughter. They're trying to play an oh-so-serious scene with an actor wearing a shirt, a tie, and boxer shorts.
Revealing mistake: 1970: When the sheriff knocks, Jeb opens the antique shop door and the jangling shop bell falls off and crashes to the floor. They pretend that nothing happened and go on with their lines.
Revealing mistake: 1967: Dr. Woodward struggles with a stuck zipper on an oxygen tent. When the prop refuses to cooperate, he makes a disgusted sound and adlibs to his companion, "Zip that up, will you, Julia?" Then he hurries out, leaving a bewildered Julia to deal with a supposedly critical patient.
Revealing mistake: 1795: Ben, complaining that Angelique is always watching him, backs into a large, tall tree trunk in the cemetery. The "tree" wobbles and sways when he bumps it.
Revealing mistake: 1897: Quentin walks away from Trask and exits through the door under the stairs. Unfortunately, that door was undersized, and David Selby was 6'2" tall. Quentin bangs his head on the doorframe hard enough to produce an audible thump.
Revealing mistake: 1990s: When Barnabas and Julia time travel into the 1990s, they find Mrs. Johnson's body tied to a tree. While a crazed Carolyn accuses them of killing her, the "corpse" blinks several times.
Revealing mistake: David is trapped in the Collins mausoleum, but doesn't yet know about the moving stone in the stairs that will allow him to open the door. At one point he moans and lies down on the stairs, which causes the "heavy" stone to flop around. He gently moves it back.
Revealing mistake: 1967: The dying Dr. Lang fumbles with a reel-to-reel recorder, making a tape that we'll hear over and over again later on. Only he "records" his message with the machine turned off: the reels aren't moving.
Revealing mistake: 1968: Jeff Clark runs terror-stricken out of a cemetery and accidentally stumbles over a tombstone. The 'granite' marker falls over with a hollow thud.
Revealing mistake: 1795: When an angry Lt. Forbes rushes out Collinwood's front door and tries to slam it, the flimsy set door not only doesn't slam, it bounces back open. The supposedly in-a-hurry lieutenant comes back and gently re-closes the door.
Revealing mistake: 1968: A shot of Barnabas and Julia taken through the small window in the cellar door apparently obscured Jonathan Frid's view of the all-important red light. Obviously thinking himself off-camera, Frid took a moment to clean the inside of one nostril with his index finger.
Revealing mistake: 1968: Adam approaches David in the woods, and brushes against a large shrub. The bush teeters and then falls over with an audible crash.
Answer: It's probably episode 193 (even though the slate at the beginning says 58). It's the episode with Sam demanding that Roger return his paintings. Three clues from the Dark Shadows Companion and from the comments of Kathryn Leigh Scott and Louis Edmonds all agree that 1) Scott is in the episode and is done for the day prior to Edmonds without his pants; 2) Edmonds is wearing a smoking jacket, and 3) Edmonds is leaning on the mantle (which is actually the cabinet where the liquor is, because the fireplace mantle is too high to lean on and the bench in front of it prevents getting too close to). There are several "breaks" in the lengthy scene where commercial were probably inserted, and all of the shots are above the waist. The previously mentioned episode 54 has Edmonds in a suit and Scott isn't in the episode; episode 54 doesn't have Edmonds or Scott; and episode 86 only has Edmonds in a suit.
Lou Edmonds was a consummate actor and would not forget that he had a lengthy scene to perform. Rather, in Episode 86, Edmonds more understandably forgot that he had to perform one last 15-second scene (a simple toast). He had removed his shoes and pants before he was reminded of the final, brief shot, and he hurried back to complete it.
Charles Austin Miller