Revealing mistake: It would seem that with the incredible advanced knowledge and furnishings that have been bestowed upon the Imorg down below, the 'Teacher' should have at least provided them with adequate high tech structuring and not the ratty, torn and warped substandard sheet rock seen on the bottom of the walls in these two camera shots. Yep, they can remove and restore a brain but can't find a place to buy good quality plasterboard. (00:23:40 - 00:33:51)
Is There in Truth No Beauty? - S3-E5
Revealing mistake: During the fight in engineering, Marvick's kick, throwing one of the engineering crewmen violently back against the wall, misses by an obvious mile. (00:20:10)
Is There in Truth No Beauty? - S3-E5
Revealing mistake: The colorful nebulae of the energy barrier are showing through the hull of the suddenly-transparent Enterprise as it heads back into the galaxy. (00:37:40)
Revealing mistake: Chekov covers Mara's mouth with his hand when he assaults her in the corridor. Kirk intervenes and throws Chekov against the opposite wall. Brown streaks form where Chekov's hands hit the wall, most likely from the brown makeup used to create Mara's skin tone. (00:32:20)
Revealing mistake: McCoy's stunt double's face is visible several times during the fight with the berserk orderly in the sickbay lab. (00:19:15)
Revealing mistake: At the end, a special effects matte flaw causes the rear tip of the starboard side nacelle to vanish briefly as the Enterprise orbits Scallos. (00:45:50)
Revealing mistake: In the Enterprise lab, as a sped up Spock goes to move away from McCoy and Chapel, McCoy's eyes follow his movements rather than looking at where Spock was supposed to be after he "disappeared."
The Empath - S3-E12
Revealing mistake: When the Vian fires his weapon at Kirk after the crew finds Gem, Kirk flies backwards. At this point, Kirk is not William Shatner but a stunt double.
Revealing mistake: During the battle scene, the use of special effects stock footage of the view screen, as seen over the helm from the opposite side of the bridge, briefly turns the short, brunette Ensign Chekov into a tall, thin blond guy. (00:44:20)
Revealing mistake: When Marta kisses Kirk, her hands leave green make-up smeared all over the left shoulder and back of his uniform tunic. (00:22:05)
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: 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
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: 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
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.
Requiem for Methuselah - S3-E19
Revealing mistake: When Spock examines the unknown Brahms waltz, we get a close-up of the music. Unfortunately, the hand-written score bears no resemblance whatsoever to the piece Spock has just played, though he expressly identifies it as such. (00:19:10)
Requiem for Methuselah - S3-E19
Revealing mistake: As Kirk pulls the shroud away from the Rayna duplicate, look closely at the part of her head just below her left ear. The bald cap she wore to conceal her hair and give her an unfinished look.
Revealing mistake: Due to close-ups that were cut in backwards, Kirk appears in reverse, with his uniform insignia on the wrong side, twice in this episode: once in the corridor outside sickbay, and again near the shuttle craft on Eden. (00:18:15 - 00:46:55)
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.