The Trouble With Tribbles - S2-E15
Continuity mistake: Towards the end of the episode when the Enterprise is moving leaving from the starbase, the ship is at an angle to the camera pointing to the right of the screen. The starbase behind it gets smaller and goes up a little. If the Enterprise were leaving the starbase at that angle, the starbase should have moved to the left and then completely off the screen.
A Piece of the Action - S2-E17
Continuity mistake: Though the name is spelled "Oxmyx" in the script and pronounced as such in the episode, a poster in Krako's office spells his rival's name as "Okmyx." (00:18:50)
Continuity mistake: Why does Kirk think a being of pure energy is "impossible?" They've encountered several such creatures in the past in "Metamorphosis," "Obsession," and "Wolf in The Fold."
Continuity mistake: Kirk punches the Imperial crewman that helps him in the face, but when the guy falls on the ground he's holding his side.
The Trouble With Tribbles - S2-E15
Continuity mistake: Mr. Leslie appears as one of the guards in the space station, Stardate 45XX.X. Unfortunately, he was killed in 'Obsession,' Stardate 36XX.X. External websites have a variety of excuses for this miraculous reappearance, but he very definitely dies in the show, with no canonical reason for him reappearing beyond it being a mistake.
Continuity mistake: In a few episode we'll hear about "Hodgkin's Law of Parallel Development," but here Spock claims the odds of a planet developing similar to Earth's Nazi culture are "virtually impossible." Why was it so likely as to be easily accepted there, but impossible here?
Continuity mistake: A subtle mistake, but when Spock is lying on the table in sick bay and recovers, the readings on the monitor are in the normal range. However Spock, as a Vulcan, produces very unusual readings on the monitors in other episodes.
Continuity mistake: Just before T'Pring calls for the challenge, there's a wide shot of her going toward the gong. Then they cut to a closeup and she is standing beside Stonn, and then she starts moving toward the gong again.
A Piece of the Action - S2-E17
Continuity mistake: In the very first scene after the intro, when Bela's goons hold the landing party at gunpoint, Spock's position on the sidewalk shifts back and forth from standing on the other side of a wooden bench to standing alongside Kirk and McCoy with no bench in between. In fact, in the latter shots, the bench has moved all the way across the street. (00:04:50)
Continuity mistake: At the end, when Kirk and Garrovick are beamed up seconds before the explosion, Kirk is holding his communicator up to his mouth with both hands. But when they finally materialize on the Enterprise, Kirk's hands are down at his sides: no communicator in sight. (00:47:00 - 00:48:10)
Continuity mistake: The aging Kirk's hairline has receded considerably. When he ages still more and goes completely gray, however, the receding process inexplicably reverses itself, and he suddenly has much more hair on his forehead than before. (00:34:35 - 00:43:55)
The Trouble With Tribbles - S2-E15
Continuity mistake: Kirk is holding three large tribbles while talking to Uhura on the bridge. After McCoy enters, the tribbles keep changing positions in Kirk's hands as the shots cut back and forth. (One on top and two underneath, then two on top, etc.). (00:31:45)
A Piece of the Action - S2-E17
Continuity mistake: While Kirk and McCoy attack the other two henchmen, Spock shoulder-pinches the card-playing gangster. In the very next shot, Spock's position has jumped from behind the now-unconscious man to several feet away, where he is bending over to retrieve the guns from the floor. (00:16:30)
The Gamesters of Triskelion - S2-E16
Continuity mistake: At the end, the freed thralls, including Kirk, Chekov and Uhura, remove their collars and throw them onto the game platform. But when Kirk and his crew beam away, the collars have all disappeared. (00:48:40)
Who Mourns for Adonais? - S2-E2
Continuity mistake: Apollo's lightning bolt throws Scotty across the table and dislodges a big bunch of green grapes from the fruit bowl. They fall onto the table. But when Kirk's crew later assemble at the table, the green grapes aren't there, or in the bowl, or anywhere in the temple. They magically reappear in the bowl just after Spock gets through to Kirk on the communicator. (00:18:55 - 00:41:10)
The Trouble With Tribbles - S2-E15
Continuity mistake: When Kirk is standing in the huge pile of tribbles, he's cradling two large tribbles in his arms in full shots, but only one, and in a different position, in close-ups. (00:40:00)
Continuity mistake: Kirk's arrow strikes the Klingon in the knee. But a few shots later, the shaft is protruding from his thigh, several inches above its original position. Still later, he's holding one hand to his calf just below the knee, which isn't where the arrow was either time. (00:43:40)
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.