Revealing mistake: As Kirk turns to run on the castle steps, an iron bar barricade appears, blocking his path. When it does, watch the castle wall, and the barricade. It seems to slide just a few inches to line up correctly in the shot, showing poor editing.
Continuity mistake: After swiping at Trelane to score a hit, which Trelane avoids easily, Kirk throws the sword away, which hits a bush as it falls. When Trelane calls up another sword, the bush suddenly stops moving.
The Corbomite Maneuver - S1-E11
Continuity mistake: While beaming to the alien ship, McCoy has his hands on his knees. When materializing, they are beside his thighs.
The Corbomite Maneuver - S1-E11
Revealing mistake: In Kirk's quarters, as he touches the desk top comm panel, it noticeably slides a little rather than being fixed in place.
Mudd's Women - S1-E7
Visible crew/equipment: In the briefing room, as the camera moves to its left along the seated figures, the camera rig is reflected in the glass of the communication view screen.
Mudd's Women - S1-E7
Continuity mistake: In the briefing room, after Mudd is forced to give his real name, the screen lights up with his record of offenses. In the picture, his image has the ear bauble on the right ear, but he wears it on the left.
Where No Man Has Gone Before - S1-E4
Revealing mistake: The readers in Sick Bay are supposed to be display screens, a type of CRT, for reading material. Mitchell turns his off to rest, but the words are still plainly visible.
Where No Man Has Gone Before - S1-E4
Visible crew/equipment: As the camera is close up on Kirk, and as he addresses the ship, the shadow of the boom mic plays on Smith's neck. (00:04:35)
Where No Man Has Gone Before - S1-E4
Continuity mistake: As Kirk, Spock and Mitchell exit the lift, Yeoman Smith is by the door and begins to follow, and an un-named guy walks by her and into the lift. In the wide shot of the bridge, the actions of Smith and the crewman are repeated.
Where No Man Has Gone Before - S1-E4
Continuity mistake: After Mitchell relieves him, Mr. Alden walks past Yeoman Smith. As he does, he suddenly disappears as Kirk is sitting in his chair. (00:03:55)
Other mistake: The red alert light at the entrance to the chapel blinks a few times and stops, even though the rest are still flashing. Also, the last thing Kirk says is "All decks, condition red", which is unnecessary, since the red alert has already begun sounding.
The Man Trap - S1-E2
Audio problem: As Kirk low crawls behind some boulder and grass, his communicator flips open and closed. If it was opened, the sound of the channel opening should have been heard, but wasn't. (00:36:35)
Continuity mistake: In the first scene when Spock is piloting the shuttle craft out of the Enterprise and into space, as the bay doors open you can see both the ship's shuttles, the Galileo, and right behind it the Columbus. Yet as soon as the Galileo clears the bay doors, in the immediate reverse shot, the bay is empty and the Columbus has disappeared. (00:01:45)
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.