Operation -- Annihilate! - S1-E30
Continuity mistake: When Uhura tells Kirk that she's made contact with his private transmitter she's seated at the communications console, with the two overhead screens above her station, beside the turbo lift alcove. Yet after the contact's been broken, when she tells Kirk, "It's impossible at the moment because they stopped broadcasting," in this unusual shot facing Uhura the turbo lift alcove is not behind her - Uhura is actually seated much closer to Spock's station, note the upper section with overhead screens. Then she's properly seated at her station once again.
Character mistake: Kirk informs Spock via communicator the Horta is ten feet from him, and Spock insists Kirk kill it. First, both know they cannot kill it with their phasers, and second, Spock's demand for Kirk to kill the Horta runs counter to the Vulcan philosophy of respect for all life. Spock would never want to harm, let alone kill, another life form.
Continuity mistake: As Kirk speaks with Commisioner Ferris, Kirk's hands go from holding a piece of equipment to being straight down by his side, back to holding the equipment.
A Taste of Armageddon - S1-E24
Plot hole: The ambassador and his aide beam down to the planet. This would not be possible because earlier on Scotty refused to lower the screens/shields until the Captain told him to do so. It had already been established in an earlier episode titled "Arena" that transporters don't work with screens up. (00:32:40)
Factual error: Trelane has been watching Earth as it was 900 years ago (14th century in the film), but his style is more 17th century, and he mentions Napoleon who lived in the 19th century.
This Side of Paradise - S1-E25
Continuity mistake: When Kirk and Spock successfully activate a subsonic transmitter, it cuts to a closeup of a spade's metal blade breaking the soil ground, but in the next wide shot Sulu and DeSalle are using two spades made entirely of wood. (00:44:45)
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: In the beginning Chekov disappears off the bridge for a moment and is replaced by a blond haired crew member, then he returns.
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: When Lokai leaves the bridge near the end of the episode, when he goes into the turbolift on the bridge he heads right as soon as he enters, giving away the fact that this is not a small enclosed area. (00:45:45)
Other mistake: After Chekov goes beserk on the bridge and Dr McCoy and Scotty restrain him, Spock enters the scene and grabs Chekov by the sides of his face. His hands are close together as a human's face is around eight inches wide. When the camera cuts to Chekov's perspective view of Spock, Spock's arms are spread way far apart. Either Chekov's face has ballooned to over two feet wide or Spock is grasping the Panavision camera by its two sides. (00:14:34)
Revealing mistake: When Kirk and Miri are in the kid's hideout, Kirk is attacked by Louise, the wild woman. After Kirk knocks her off his back, she falls to the ground and tries to get up again, Kirk has to resort to stunning her with his phaser. The blue beam starts coming out then starts coming back towards the phaser before going back out again. (00:26:12)
Tomorrow is Yesterday - S1-E20
Revealing mistake: Traveling towards the Sun and away from the Earth, parts of the Enterprise are missing due to superimposing the model into the current shot. As the Enterprise goes by, one of the warp engines seems to be disintegrating at the rear. (00:42:05)
Continuity mistake: While Flavius guides Kirk, Spock, and McCoy to the city to find Merik, the foursome stop behind a group of trees. In the first wide shot, as Flavius explains they'll wait until dark, there are no red marks on the tree trunks, but in their closeups there are a few red marks (presumably from squibs), before the gunfire has even occurred. At the start of the second wide shot the tree trunks are still void of those marks, and when the police shoot at them that's when the red marks appear. (00:15:15)
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)
Is There in Truth No Beauty? - S3-E5
Deliberate mistake: While Miranda is with Kollos, McCoy tells Kirk that he didn't reveal her secret because he respects her privacy, then when Miranda steps out of the room and concedes to obey, the next closeup of Kirk is a flipped shot. (00:34:05)
Shore Leave - S1-E16
Visible crew/equipment: While Kirk is with Spock, when Finnegan shows up again Jimmy boy gives in to the chase, then as Finnegan runs and shouts, "Here I am," the shadow of the camera equipment is visible at the bottom right side of the screen, as it follows Finnegan. (00:35:55)
The Gamesters of Triskelion - S2-E16
Other mistake: When Kirk agrees to fight in the arena at the end of the episode, he and the thralls are warned that touching an opponent's color will result in the loss of a weapon. Kirk does this several times during the fight, but isn't penalized in any way.
Continuity mistake: When McCoy places the old tricycle down on the ground, the handlebars are facing the right with its wheels facing the left. When McCoy is attacked by the diseased Only, Kirk and Spock subdue him, and as he lies on the ground the tricycle flips over between shots, so the handlebars suddenly end up facing the left. (00:04:30)
The Immunity Syndrome - S2-E18
Continuity mistake: When McCoy escorts Spock to the shuttlecraft hangar McCoy is wearing his short-sleeved medical tunic, but when Spock suggests that the doctor could wish him luck, in the next closeup McCoy is wearing his long-sleeved uniform. (00:29:40)
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)
Suggested correction: At this point they don't have any proof that they can't kill it, and since Kirk is in danger, it's logical to try. Also, Spock is half human and he's concerned about his best friend being killed. Logical or not, he'll want Kirk to protect himself at all costs. Other episodes have shown where Spock doesn't always behave logically when his friends are at risk and he lets his emotions come out.
envisaged0ne