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: 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)
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.
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)
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: 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)
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.
Continuity mistake: As Gary Seven beams in, Scotty's hair changes between shots.
The Gamesters of Triskelion - S2-E16
Revealing mistake: As the camera does a close up of the Master Thrall, the line of the bald skin cap is visible. (00:05:10)
Continuity mistake: When Mr Hengist goes on the rampage in the hearing room, Kirk pushes Yeoman Tankris behind him. However, when we see Kirk punching Mr Hengist in the jaw in the next shot, Tankris is missing, and in the shot after that, she is back again.
Continuity mistake: When Nomad first appears on the bridge, the indicator light on Scott's communicator panel is on. A second later, it's off, and he turns it on to say his line.
Revealing mistake: A number of times through the episode, the wire holding Nomad up and moving it around is visible. Example: When Nomad first moves off the transporter pad, look directly above it; the black wire can be seen in front on the light over the pad.
The Gamesters of Triskelion - S2-E16
Other mistake: Kirk tosses the Andorian, and as he hits the ground, his shirt comes up and the man's real skin tone is visible.
A Piece of the Action - S2-E17
Visible crew/equipment: When Kirk and Spock pull up after their first car ride, a boom microphone is visible in the reflection from the passenger-side spare-tire cover, which is chromed. As Spock gets out, the mic moves away.
Continuity mistake: As Decker is talking about the Planet Killer, the camera looks at McCoy. His left eyebrow is slightly arched, and his hair is styled differently. It can be seen that this shot is reversed from normal.
Continuity mistake: After Spock talks about Sun Worship on the bridge, Uhura goes to correct him. As she's sitting at her console, her arm is covering the note board. When the angle changes to include her, Kirk, Spock and McCoy, her arm is above the note board. Back to a close up, and her arm's covering it again.
Continuity mistake: When Kirk, Bones and Spock are commanded to stop, and raise their hands, they do so. After a moment, Kirk starts to lower his hands. After the camera cuts to a shot from behind, Kirk's hands are by his sides and he goes for his phaser. After another warning shot, he says "I think he means it." The camera goes back to facing them, and his hands are up again.
Continuity mistake: After Gary turns on the typewriter and tells Roberta to give her report but not with her fingers, she responds, "Well, how do you expect me to type, with my nose?" But the typewriter types, "How do you expect me to type, with my nose?" omitting the "Well." It didn't edit her question, because we see from the rest of the scene that it types absolutely every word she says until Gary turns it off. (00:17:45)
Answer: Kirk was getting his physical and Dr. McCoy probably turned off communications, because if he hadn't, Kirk would have left and headed straight for the bridge, leaving McCoy irritated.