A Taste of Armageddon - S1-E24
Continuity mistake: At the door, as Spock gives Yeoman Tamura her orders, his hands are in front of him. In the close up, they are suddenly by his sides.
A Taste of Armageddon - S1-E24
Revealing mistake: It is easy to tell where the matte painting and live action area meet when Fox and the assistant appear.
This Side of Paradise - S1-E25
Continuity mistake: Kirk threw a "spore flower" across the bridge and it landed towards the front of the bridge. Later on, Kirk returns to the bridge and despite all the crew being on the planet the flower is gone. (00:28:20)
This Side of Paradise - S1-E25
Continuity mistake: As Spock beams up from the planet, Kirk, who is manning the transporter controls suddenly pulls a steel pipe from nowhere. (00:33:55)
This Side of Paradise - S1-E25
Continuity mistake: When Kirk and Spock successfully activate a subsonic transmitter, it cuts to a closeup of a spade's metal blade breaking the soil ground, but in the next wide shot Sulu and DeSalle are using two spades made entirely of wood. (00:44:45)
This Side of Paradise - S1-E25
Plot hole: When Captain Kirk is the last person unaffected by the spores, he's on the bridge lamenting the fact that he is trapped in orbit above the planet since he can't pilot the ship alone. He also can't call for help because Lt. Uhura sabotaged long range communications. but Captain Kirk has somehow forgotten about the shuttle craft. He could have easily escaped on one of those.
This Side of Paradise - S1-E25
Continuity mistake: As Kirk sits on the deserted bridge, there is nothing out of the ordinary with him. After he sits at the helm position, the camera looks at him over the console, and there's suddenly a spore spewing plant to shoot him.
Suggested correction: The plant did not suddenly appear, it was there from earlier in the episode.
This Side of Paradise - S1-E25
Other mistake: After Spock is hit with the spores, he goes down on all fours in pain. As he writhes around, the skin tone of his ears is vastly different to his other makeup.
This Side of Paradise - S1-E25
Other mistake: As Spock and Kirk are fighting, Spock bends a steel bar with one of his blows. When he hits Kirk, though, it simply makes Kirk a little sore. A blow strong enough to bend a steel bar would shatter human bones.
This Side of Paradise - S1-E25
Continuity mistake: As Spock and Kirk are fighting, Spock pushes Kirk to the wall after bending the bar with his first blow. The bent bar falls to the ground and ends up against the wall by Kirk’s feet. Moments later, the bar is nowhere to be found.
Character mistake: Shatner fluffs his line when asking the mining engineers whether they've posted sentries. He asks if they've posted "centuries" instead. (00:05:20)
Deliberate mistake: Here, as in nearly every other ST episode featuring caves, caverns or mines, all the floors are perfectly flat and the lighting adequate-to-see-by or even brilliant. These configurations are easily found on soundstage sets - but not in nature. (00:16:30)
Revealing mistake: The Horta's round tunnels have perfectly even striations and are obviously factory-manufactured tubes. Acid secreted by an elliptical creature burning through solid rock would not create a perfect circle. The Horta is visibly not chewing, sculpting or smoothing the sides. No acid burning method would leave patterned stripes on the walls, either. (00:18:15)
Continuity mistake: When Kirk is facing the Horta he has his phaser in his right hand when seen from the front but when seen from behind he has his communicator in his left hand and no phaser. (00:31:00 - 00:38:00)
Revealing mistake: When Kirk holds a golden egg, a seam can be seen on it. (00:43:55)
Revealing mistake: A straight and level seam connecting the top and bottom halves of the tunnel Spock is crawling through is visible.
Suggested correction: Views of the tunnels made before the creature was wounded by Kirk and Spock appear almost perfectly smooth. It is explained that the creature exudes a powerful acid to dissolve the rock. This tunnel was made after the creature was wounded, so it is logical that the wounded portion of the creature would secrete less acid thus leaving an imperfection as the creature tunnels. This could be a case of incredible attention to detail by the set designer rather than an error revealed.
This correction is too much of a stretch to explain a perfect seam by the wounded Horta. Plus, if the Horta was secreting less corrosive substance, then that area would be less eroded, not more. If attention to detail was paid, then the area would have an outward seam, not an inward one.
Character mistake: Spock says that Vanderberg said there were thousands of these silicon nodules, but Vanderberg actually said there were millions of them. Not a mistake Spock would make.
Character mistake: When Spock and Kirk pursue the Horta, they come to a fork in the tunnel. Kirk points right and tells Spock to go left. Then he points left and says he'll go right.
Continuity mistake: After his initial mind meld with the horta, Spock tells Kirk, "That's all I got, Captain: waves and waves of searing pain." A minute later, he says that it's "a highly intelligent, extremely sophisticated animal" that calls itself a horta. Apparently, waves of searing pain were not all that he got after all. Unlike Spock to be so imprecise.
Plot hole: Spock has absolutely no way to know, yet, that the horta only secretes her corrosive substance when tunneling: he hasn't had time to examine her or to do more than determine that she does indeed secrete a substance that cuts the tunnels. So he should at the very least scan the piece of her that falls off before he picks it up with his bare hands. Major lapse of logic, which given his character goes beyond a character mistake.