The Enterprise Incident - S3-E2
Plot hole: Despite the Romulan ships keeping a close watch on the Enterprise, when they beam the disguised Cpt Kirk over to the Romulan vessel it goes undetected.
The Trouble With Tribbles - S2-E15
Audio problem: Near the end of the episode, Kirk asks Scotty where the Tribbles are. Scotty approaches him and says, 'I used the-' before the shot cuts to a close-up of him saying '-transporter, Captain'. In the wide shot, his mouth doesn't move. (00:48:42)
The Man Trap - S1-E2
Continuity mistake: About 40 minutes into the episode during the meeting discussing what to do with the creature, "Nancy," disguised as Dr. McCoy, has their arm by their collar, but in the next shot, "Dr. McCoy" has their arm resting on the table.
The Man Trap - S1-E2
Continuity mistake: Spock is standing hunched over a control panel; however, in the next shot, he is suddenly sitting down with not enough time having passed for him to take a seat.
The Man Trap - S1-E2
Continuity mistake: When the salt vampire changes from the Swahili crewman to "Nancy" outside Dr. McCoy's quarters, the background changes. Note the red panel on the wall. (This has nothing to do with a height difference, since it's the angle that changes.)
The Man Trap - S1-E2
Revealing mistake: When Sulu touches the dead Barnhard's face, the dead face twitches.
The Man Trap - S1-E2
Revealing mistake: Throughout the episode, the difference between the actor's real ear and the prosthetic point is very obvious. Note the scene at the beginning in the conversation between Spock and Uhura; the difference in Spock's makeup from the real and fake ear is very obvious.
Continuity mistake: As Kirk and Spock head towards the Only, they first approach him from the same side. When the camera cuts to a different angle, they are approaching from different sides. (00:05:09)
Character mistake: Elaan says "If I have to stay here for ten light-years..." A light year is a measure of distance. (00:24:03)
The City on the Edge of Forever - S1-E29
Factual error: The song "Goodnight Sweetheart" was written and first performed in 1931. This episode takes place in 1930, one year before.
Tomorrow is Yesterday - S1-E20
Character mistake: Kirk introduces Spock as "Lieutenant Commander Spock," but Spock is obviously wearing full commander's stripes on his uniform.
Visible crew/equipment: After Uhura asks McCoy if she'll become like Chekov, McCoy reassures her about finding an antidote. Then, when it cuts to Engineering, there's an actor's black tape mark and a chalk T-mark visible on the floor. (00:38:10)
Continuity mistake: When Kirk beams down to the planet, he selects the front transporter pad next to the steps, and closest to the door. When he materialises in the replica transporter room, he is on the same pad. When the scene cuts to a view of the empty transporter room, Kirk is no longer on the front pad. The scene cuts again, and Kirk steps off the front pad to walk to the control panel. (00:00:30 - 00:01:30)
And the Children Shall Lead - S3-E4
Audio problem: When Spock asks Kirk, "Why are they bothering Starfleet?", there is a loud buzzing noise twice as they are focused on Kirk's face.
The Conscience of the King - S1-E14
Continuity mistake: When Spock explains to McCoy his theory of Kodos' use of eugenics, the background behind Spock is a wall of red grating, but the shots of Spock speaking to McCoy alone (McCoy isn't in the shot) show a blue background wall with a control panel on it. (00:21:55)
The Conscience of the King - S1-E14
Continuity mistake: As Kirk asks the Enterprise's computer about the history of Anton the Actor and Kodos the Executioner, his hands change positions from being away from the computer's controls to near them, then clasped as the shots quick cut.
Who Mourns for Adonais? - S2-E2
Continuity mistake: In the original version, the giant hand is holding the Enterprise for most of the episode, but when the Enterprise fires phasers at Apollo's temple, the hand is gone.
Continuity mistake: When Scotty thwarts Garth, disguised as Kirk, attempts to beam to the Enterprise using the Queen-to-Queen level three code, Kirk throws a tantrum and accidentally loosens one of his controls during his rant right before he turns back to Garth.
Suggested correction: How is that a mistake?
Continuity mistake: When the Enterprise tries to escape Gothos, and the planet blocks the ship's path each time, Gothos is very transparent, where the stars could be seen through the planet.
Continuity mistake: After Spock nerve pinches Chekov when he goes mad and he is taken to Sickbay, the Tholian ship appears and hails the Enterprise. When Spock says "on main viewer," the shot of Loskene is on the screen, but the back of Chekov's head can be seen when it should be in Sickbay.
