Let That Be Your Last Battlefield - S3-E15
Revealing mistake: Because stock special effects footage was used, the shuttle supposedly "stolen from Starbase 4 two weeks ago" is plainly marked "Galileo, NCC 1701/7, USS Enterprise." (00:02:15)
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)
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)
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: Due to the use of stock footage once again, Sulu's console viewer appears and disappears repeatedly throughout the episode. (00:08:45)
Let That Be Your Last Battlefield - S3-E15
Continuity mistake: The planet Cheron is blue the first two times we see it on the view screen, but when the Enterprise enters orbit, and every time we see it thereafter, the planet has mysteriously turned red. (00:44:05 - 00:46:00)
Let That Be Your Last Battlefield - S3-E15
Other mistake: At the end of the episode, as Lokai is running through the ship, his hands are empty. However, in one closeup shot he is holding onto a rope with his left hand. The rope is gone in the following shot. Presumably this rope was used to tether him to the camera as he ran so that he could maintain distance from the camera.
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: As Kirk turns all the way around to look at the newly arrived Bele, the shadows of the stage wiring is easily spotted at the top of the screen.
Let That Be Your Last Battlefield - S3-E15
Other mistake: When preparing to go around again, Sulu and Checkov start working their controls. When there is a close up of Sulu's hand, it's obviously a re-used shot of Kirk's hand starting the 30 second count down timer on the Constellation in "The Doomsday Machine" (S2 E6).
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: After Kirk shuts down the self destruct, he asks Spock if the ship is heading for Arianas. At one point in the dialog, you can see the display for the self destruct sequence is still on the screen, just not lit up.
Let That Be Your Last Battlefield - S3-E15
Revealing mistake: When the camera is close up on Beal's face, you can see a bit of real flesh color where the black and the white greasepaint used didn't quite match up.
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.