Visible crew/equipment: While Kirk and Spock are being chased, McCoy hears the gunfire so he stands up and walks away from the rock, then just as McCoy stops to use his communicator to contact Enterprise, the ground microphone is visible at the bottom, left corner of the screen. (00:02:30)
Continuity mistake: The gash on Kirk's right cheek disappears between the time he and McCoy fall asleep in the cave and when McCoy wakes up to find Kirk at Nona's side. (00:21:30 - 00:23:15)
Revealing mistake: Kirk jumps across the burning hot forge to hide from the people approaching him, only problem is that he actually touches the red hot coals with the palm of his hand. Somehow he managed to avoid serious burns. (00:31:15)
Continuity mistake: When Nona is trying to seduce Kirk, we see a close-up of him with nothing on his shoulders. Cut to a two-shot and suddenly Nona's arms are over his shoulders and around his neck. (00:41:00)
Revealing mistake: While Nona is struggling with her Villager attackers, the camera tilts just far enough to show, in the distance, a nice (if slightly smoggy) view of buildings, docks and boats in Santa Monica Harbor. (00:45:00)
Deliberate mistake: After one of the enemy villagers stabs Nona, during the ensuing fight when Kirk does a flying dropkick on a villager, this semi-closeup and the next wide shot are both flipped shots - the leather band is on Kirk's left upper arm, instead of his right. (00:46:15)
Continuity mistake: In the original version, the planet is the same as the one used in "Bread and Circuses", but when the Enterprise leaves orbit at the end, it is a totally different planet, as it is the one used in "Friday's Child".
Visible crew/equipment: When Scotty joins Thalassa while she's working, she asks if he has "prepared the megaton hydrocoils," and the shadow of the boom mic can be seen moving at the top of the screen. (00:33:20)
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."
Visible crew/equipment: After Melakon shoots at the curtained window and kills John Gill in the broadcast booth, Isak shoots Melakon, then when Eneg stops the soldier who points his gun at Isak, the shadow of the boom mic dips into view at the top, left side of the screen. (00:45:50)
Revealing mistake: In the jail cell scene, when Kirk tears a strap from the bed, his left handcuff is open. It remains open for several seconds, while he tries to conceal it by moving his right hand to block the camera's view.
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?
Revealing mistake: After being put in the cell, when the camera is in a closeup of Spock, you can see the lines in the prosthetic ears, and can easily tell where the makeup is blended into his real ear.
Continuity mistake: The blood dripping from Isak's mouth changes sides.
Revealing mistake: As Kirk and company exit through the tunnel, the seams of the wall sections are visible.
Other mistake: In the cells, the particular strip of metal Kirk pulls loose has rivets that are noticeably different than the rest, making it easier to pull loose.
Deliberate mistake: When Rojan asks Kelinda if she wishes to remain with Kirk, she replies that although Kirk is "most interesting" she wishes to go with him, and the next closeup of Rojan is flipped. (00:48:15)
Continuity mistake: When Scotty gets drunk and tosses an empty bottle away, there's a dubbed in sound of glass breaking, but when he collapses, the bottle is unbroken at his feet.
Continuity mistake: Kirk and McCoy are in the Exeter's engineering section when Kirk uses the intercom to ask if anyone is aboard. Several shots of the deserted ship follow as his voice echoes off the walls, including one of engineering - with Kirk and McCoy suddenly, mysteriously absent. (00:03:45)
Continuity mistake: When Kirk and McCoy join Spock and Galloway on Exeter's bridge, McCoy kneels down and uses his med tricorder with its strap crossed over his shoulder, but in McCoy's closeup the strap is gone, then next shot the strap is once again over McCoy's shoulder. (00:04:25)
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.