Continuity mistake: Kirk and the others are beamed down to the planet, and when the Enterprise crew are led into Mudd's throne room by two Alice androids (the Alice series are 500 identical androids) they are wearing the usual metallic, backless, kitten heel slip-ons, but in the next shot android Alice at the left is now wearing altogether different shoes - cream color with ankle-straps. (00:09:30)
Visible crew/equipment: After Garrovick is relieved of his duties, Kirk tells McCoy and Spock to make comments and recommendations in their reports, then Garrovick returns to his quarters. Just as Kirk exits the turbo lift on the bridge, the boom mic is visible at the top, left side of the screen. Then when Kirk apologizes to Scotty, in the next wide shot two pieces of filming equipment are visible at the top of the screen. (00:17:20)
Visible crew/equipment: After Kirk hits Kras with an arrow Spock's arrow hits a Capellan on the cliff, and when the Capellan falls into the bush, a crew member wearing sunglasses and a white T-shirt is visible at the left side of the screen. (00:43:50)
Visible crew/equipment: While Kirk and Spock are being chased, McCoy hears the gunfire so he stands up and walks away from the rock, then just as McCoy stops to use his communicator to contact Enterprise, the ground microphone is visible at the bottom, left corner of the screen. (00:02:30)
Continuity mistake: When Spock shows the others the machine which must be put "in the proximity of the Companion", in the closeup Spock's left arm is up on the machine and we see the chair opposite Spock is empty. However, in the next shot Spock's right arm is up by the machine and Kirk is sitting in that chair. (00:22:10)
Revealing mistake: In the jail cell scene, when Kirk tears a strap from the bed, his left handcuff is open. It remains open for several seconds, while he tries to conceal it by moving his right hand to block the camera's view.
The Trouble With Tribbles - S2-E15
Revealing mistake: When Kirk finds his position on the bridge occupied by the Tribbles, he calls for Dr. McCoy, and as he arrives, Kirk thrusts some of the Tribbles under his nose. In the shots where Kirk's face is seen, one of the Tribbles he is holding features a visible seam.
Visible crew/equipment: When McCoy gives the guard a shot and he and Scotty break into Engineering, you can see a crew member's hand holding a red handle and their bare arm (it's not Scotty), who apparently is helping to open the door. (00:23:00)
Continuity mistake: When Kirk's arrow hits Kras it protrudes from his leg, but in the next wideshot as Kras screams and stumbles the arrow is quite gone from his leg, but three shots later the arrow is back in his leg while he tries to pull it out. (00:43:40)
Visible crew/equipment: At the hangar deck, after Kirk introduces Sarek to Spock and McCoy they all step forward, then as Sarek introduces his aides and his wife, the three white tape marks are visible on the floor behind them, where they had been standing. (00:02:15)
Visible crew/equipment: After Amanda tells McCoy about Spock's pet sehlat, when Sarek and Amanda walk away, the actors' multiple white tape marks are visible on the floor, under the table. (00:10:50)
Visible crew/equipment: After Kirk tells the policeman that he wants to see Merikus and "perhaps" he's a friend, the policemen lock the cell then leave, and when it cuts to a view of the cell from the side as Spock walks over to the steel bars, the overhead boom mic is visible inside the cell, over Spock. It's visible again, with a better view, when McCoy walks over to Spock beside the bars. (00:18:15)
Revealing mistake: After being put in the cell, when the camera is in a closeup of Spock, you can see the lines in the prosthetic ears, and can easily tell where the makeup is blended into his real ear.
Factual error: Kirk, McCoy, and Spock are chained to the dungeon wall, with McCoy noticing he is next to a skeleton, also chained. This is incorrect, as a skeleton's bones are held together by cartilage, which would rot over time. Therefore, the skeleton would not be hanging intact, but would be a pile of bones on the floor.
Suggested correction: As we learn in the episode, the 2 aliens created the entire castle only recently to appeal to the human's primal fears and superstitions. A pile of bones on the floor would not have the frightening impact of a hanging skeleton.
Continuity mistake: The blood dripping from Isak's mouth changes sides.
Continuity mistake: As Nomad first hears Uhura's singing, it extends antennae and leaves the room. After a quick cut scene, as it turns in the corridor the antennae is retracted, then out again on the bridge.
The Trouble With Tribbles - S2-E15
Continuity mistake: During the brawl, as Cyrano Jones watches the action, the glass he quickly raises loses most of the liquid. After he gets half way through the scene, the glass is suddenly almost full.
Visible crew/equipment: A stagehand's foot is visible before the party beams down. (00:09:10)