When Kirk first contacts the Enterprise from the cave, Spock says that they have been trying to contact him but, in the immediately preceding log entry, Spock said that any attempt to reach the Captain would endanger him, and they must remain silent.
When Plasus welcomes Kirk and Spock. he is wearing sandals. Later, approaching the staircase with Droxine, he is wearing shoes.
Kirk throws his phaser away to his right when confronting Plasus, but Vanna looks at it to her left.
During the shot of Plasus being forcibly beamed directly to Kirk's location in the mines, the bottom of the curtains behind him changes position as he transports.
The advisor appears in the cave already dirty, even though he only just beamed in, fresh from cloud city. - When the advisor is first seen in the cave, he states that he's already been there "nearly an hour of your Earth time."
When Kirk fights the High Council advisor, he strikes him and the advisor falls back and hits the cave wall/rock behind him. He actually breaks the wall and a crack forms along the edge of the rock outcropping.
When Kirk says, "The only way you'll use.... that device again.. is on one of us," He obviously almost forgot his line(s) after "use" and "again."
When Plasus and the Sentinels arrive on the platform, the Troglytes start to flee and one of them is fired upon and brought down. Two others are seen escaping into the cave, but Vanna is not seen escaping.
After the initial scuffle with the Disrupters, when Kirk says, "Who are you? What's the meaning of this attack?" his mouth does not move.
After Plasus says "I would suggest that you and First Officer Spock be our guests on Stratus," Kirk replies "Very well." However, Kirk's lip movements do not match the words spoken.
When Plasus says to Droxine "Leave here at once. Go to your music." the voice changes. It is not Jeff Corey's voice. Possibly the voice of William Shatner doing some dubbing.
Plasus rules as a cruel dictator over Ardana, suspending civil liberties and hoarding resources. This is contrary to the justice- and fairness-oriented ways of the United Federation of Planets. As Ardana is part of the Federation, the Prime Directive does not apply in the matter. Plasus is a criminal and Kirk & Spock are officers of the law. They waste valuable time negotiating and working out deals with Plasus when they have a legal obligation to arrest him and return the hoarded resources to their rightful owners.
Vanna's cell is opened by a sentinel and closed by Kirk simply by pressing a button. However, the button would be easily accessible to Vanna or anyone else locked within the cell, thus rendering it essentially useless as a detention facility.
In Amok Time (1967), Spock tells Kirk, his closest friend, that the Pon Farr is not to be discussed with non-Vulcans. Even after Kirk guesses the gist of it, Spock is visibly uncomfortable talking with him about it. Yet here, he chats about it with Droxine, a woman he has known for only a few hours, and with no more concern or discomfort than if he were discussing a new chemical compound.
Spock engages in physical combat against Vanna and her men, rather than use the Vulcan nerve pinch to incapacitate them more effectively .
When Kirk and Spock leave the bridge to beam to the planet, Scotty is not seen on the bridge to take over, and Kirk doesn't put anyone in charge.