Continuity mistake: During the fight with the Andorian Kirk was stabbed in his lower kidney region, he even holds his hand there to stop the bleeding. In sickbay later on, he has a bandage around his chest and McCoy says he has a punctured lung. (00:28:30)
Continuity mistake: Lt. Galloway, who was killed off the season before in "The Omega Glory," is resurrected without explanation for this final episode. (00:24:25)
Continuity mistake: On the first map we see of the Romulan Star Empire, the two planets are Romulus and Remus. But the map later reads "Romulus" and "Rom II."
Continuity mistake: When Sylvia angrily upbraids Korob for talking too much, an inserted reaction close-up of him makes the table and chairs change from in front of him to behind him and back between shots. (00:27:15)
Continuity mistake: Just before Kirk kicks his attacker for the final time during the fight in the corridor, the Andorian picks the knife up off the deck with his left hand. In the very next shot, the knife has instantly switched to his right hand. (00:28:30)
Character mistake: Shatner fluffs his line when asking the mining engineers whether they've posted sentries. He asks if they've posted "centuries" instead. (00:05:20)
Revealing mistake: At different points during the Metrons' transmission to the Enterprise, both Kirk and the Gorn pop into the picture a few seconds after the rocky landscape appears. (00:37:00 - 00:37:55)
The Gamesters of Triskelion - S2-E16
Continuity mistake: The Providers' representative colors on the game platform and the thralls' collars (all three colors are on Galt's collar) are red, yellow and blue. But when Kirk appears before them, the Providers themselves are red, yellow and green, and so is the gaming symbol inside their glass bubble. (00:40:00)
Revealing mistake: Near the end of the episode, after Kirk has destroyed the orb, we see Korob and Sylvia in their true form. As they move, you can see the black strings used to manipulate the puppets.
Continuity mistake: The ID cards Kirk puts into the computer to verify their identity appear/disappear in close/long shots.
Continuity mistake: The Romulan vessels fire plasma weapons (as seen in "Balance of Terror"), but when they hit the Enterprise they become photon torpedoes.
Continuity mistake: When Elaan visits engineering, the close-up shots of Scotty show a security guard wearing a black utility belt standing in the background. But the man is missing in all the full shots. (00:13:15)
Continuity mistake: Near the end, when Cloud William opens "The Book," the red bookmark ribbon isn't in the spot he turns to, until the close-up of the page, when it suddenly appears there. (00:39:15)
Revealing mistake: When Kirk & Spock beam down with Lincoln to the supposedly newly-created non-volcanic landscape, there are footprints all over the ground. They disappear a few shots later, though.
Revealing mistake: When Kirk pushes Plasus against a rock wall in the mine, a huge upper section of the "solid rock" wobbles. (00:43:20)
Requiem for Methuselah - S3-E19
Revealing mistake: When Spock examines the unknown Brahms waltz, we get a close-up of the music. Unfortunately, the hand-written score bears no resemblance whatsoever to the piece Spock has just played, though he expressly identifies it as such. (00:19:10)
Continuity mistake: When Mr. Scott asks Watkins to check the bypass valve, Watkins is facing the engineering boards with both hands on the panel. When we cut to a different angle, however, he's suddenly jumped to a position facing Scott with only one hand on the panel. (00:18:35)
Continuity mistake: Before the Capellans reach him, the Klingon's body moves into a completely different position, and to a different spot on the ground, than it was in when he first fell. (00:46:10)
Factual error: In several episodes, when the Enterprise has to turn "hard about", we see it banking to one side like a jet plane. The Enterprise has no wings, and they're in space. No banking.
The Empath - S3-E12
Continuity mistake: The bruises on McCoy's face change configuration, color and texture between the time Kirk and Spock first find him and the scene where Gem heals him. (00:34:15 - 00:40:30)
Answer: After causing Norman to overload, all of the other androids shut down. The same could be said for the androids on the Enterprise.