Deliberate "mistake": "Doomsday": The huge system and missile control boards containing the failsafe units suddenly appear on Seaview's bulkheads just for this episode. And of course, they disappear after this, never to be seen again.

Continuity: "Doomsday": Captain Crane removes a failsafe key, which is hanging outside his uniform collar, from around his neck. It wasn't there in the previous shot.

Factual error: "Invaders": The ship's doctor claims that carbon 14 dating proves the man from the undersea capsule to be 20 million years old. Not likely. Carbon 14 testing can date once-living matter only within the last 70,000 years, and is generally considered accurate only within the last 50,000.

Deliberate "mistake": "Return of the Phantom": Kroeger's ghost takes over Crane's body when the captain is injured, but still alive. In "The Phantom Strikes," Kroeger told Nelson his host had to be dead first. This "fact" needed to be altered in the sequel so that Crane could survive to be rescued at the end.

Visible crew/equipment: "The Phantom Strikes": When Nelson says, "Let's get out of here," the shadow of the entire camera rig moves by on the side of the navigation console.

Continuity: "The Cyborg": To expose the cyborg duplicate of himself, Nelson disrupts the nerve controls on the computer facsimile's left hand. But the cyborg Nelson's right hand is the one that subsequently malfunctions.

Continuity: "No Way Out": When Anna tries to kill Koslow, Victor spies on her from behind the ventilation grate. The ribbons fluttering on the duct cover disappear when the shot switches to Victor's point of view.

Continuity: "No Way Out": When Victor tries to get into sickbay, the guard stops him, pointing a rifle at his chest. But in the very next reverse angle shot, the rifle is again in its original position in the guard's hands, pointing at the ceiling.

Revealing: "The City Beneath the Sea": On the beach, Molina is petite, thin and small-chested in her wetsuit. Underwater, she mysteriously gains several pounds, bigger muscles and a much larger bust, thanks to a poorly-matched stunt double.

Continuity: "The City Beneath the Sea": Seaview's windows form 8 horizontal rectangles in 2 rows across its bow. But the interior sets have windows that form vertical rectangles, and they're much closer together than they are in the exterior shots.