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.
And the Children Shall Lead - S3-E4
Continuity mistake: The stardates of Starnes' entries are 5025.3, 5032.4, and 5038.3 But Kirk gives the stardate of when they arrive at the beginning of the episode as 5029.5, so apparently Starnes made two entries after he died.
Continuity mistake: The Organians cause all the weapons to overheat, and everyone drops them to the floor. When Kor moves to the desk to call his ship, though, he's wearing his disruptor. It's gone again when he returns. (00:41:45)
Continuity mistake: Sulu's hooded viewer is up as he reports that the Defiant is starting to drift. In the next shot, a reverse angle showing the screen, the viewer disappears. This recurs throughout the episode. (00:06:10)
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)
Continuity mistake: During the attack on the outpost, as Spock arrives in his foxhole, Kirk puts down the box of ammunition and positions the grenade launcher. We cut to a higher angle as Spock scrambles around to the Captain's left, and Kirk is putting the box down and positioning the launcher all over again. As the action was supposedly continuous, there wasn't time for Kirk to pick the items up and set them down a second time. (00:08:40)
The Return of the Archons - S1-E22
Continuity mistake: The lawgivers' robes that Kirk and Spock take off and drop on the floor just inside the doorway disappear after they phaser the wall to reveal Landru. The robes reappear a few minutes later, but have now migrated several feet to one side, bunched up against the wall where they are no longer in tripping range of the actors about to enter the scene. (00:42:25 - 00:45:00)
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.
Continuity mistake: When Kirk orders the crew to fire phasers; the exterior shots show the ship firing torpedoes, and torpedo explosions flashing out in space.
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)
Shore Leave - S1-E16
Continuity mistake: Finnegan flips Kirk over his shoulder near the end of their fight. When Kirk lands, his uniform is still completely intact, but when we cut to a close-up, his shirt is suddenly shredded. (00:38:30)
Continuity mistake: Lincoln asks Kirk if they measure time in minutes and Kirk replies "We can convert it." In every previous episode they've always used minutes - their ship chronometers are still set to minutes.
Who Mourns for Adonais? - S2-E2
Revealing mistake: When Apollo first grows large, the shimmering edge of the special effects matte is visible in the sky just above his right shoulder. (00:13:35)
Audio problem: In Zarabeth's cave, when McCoy says, "You've been dishonest with me, Spock," his lips are completely out of sync with his words. (00:42:00)
Revealing mistake: When he kicks Colonel Green away during the first fight, Kirk splits his pants. Fortunately, they mend themselves a few shots later. (00:28:00)
Continuity mistake: The leather strap with which the Troglytes lasso Spock disappears and reappears repeatedly from around his waist and shoulders during the scuffle at the mine entrance. (00:04:30)
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: Stock footage strikes again when Kirk orders the red alert. A shot of the bridge and view screen, with Kirk standing in front of his chair, once more switches Kirk out for a stand in, and Chekhov has gone and is replaced by what looks like from behind like a young woman or a man with a long neck. Also the central display between navigator and helm is now different from that earlier. (00:11:15)
The Empath - S3-E12
Continuity mistake: After partially healing him, Gem falls away from McCoy and lands, unconscious, perpendicular to the dais he's lying on. When Kirk and Spock rush over, however, she's suddenly moved several feet away and is now lying parallel to the dais. (00:44:50 - 00:45:35)
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.