As soon as an attack was discovered on the Enterprise, security would have been assigned to Karidian, who Kirk suspects of the murders. This would have cleared him of involvement in the later attempt.
The comparison between Karidian's voice and Kodos's should have been done instantly by the computer. There is no explanation for the delay.
At the end of the episode, when Lenore runs from backstage onto the stage, her hair went from perfectly coiffed, to a mussed mess in seconds.
When Lenore steals the security officer's phaser, she doesn't change the setting on it before firing. Standard procedure would have had the weapon on a stun setting, which wouldn't have killed Karidian. So why did he die?
Trivia: When Kirk is looking for the overloading phaser, he calls for a "double red alert". There is no other instance in Star Trek of such a status.
It seems a little odd that Dr. McCoy, the ship's chief surgeon, is sitting in sick bay getting drunk. He's not on shore leave and if he wanted to have a drink or two, why not do it in his quarters? It seems rather unprofessional, to say the least.
After the phaser blows up, you can see the sign on Kirk's quarters, his room number is "3F 127", in "The Man Trap", Dr. McCoy's quarters were also number "3F 127".
After Lenore kills Karidian, there is a couple of close-ups of him on the ground where he is obviously breathing.
Spock later says the computer confirmed that Kirk, Leighton, Riley, and Karidian were all on Tarsus IV during the massacre. It couldn't have done this because Karidian didn't exist until Kodos created the identity sometime after the massacre.
After Kirk meets Kodos he asks the computer how many eyewitnesses to the massacre there were that can still testify, it says "Nine." Later Spock asks the same computer the same question and it says there are only two still alive. Why did the computer say to Kirk earlier that there were nine that could testify?
The computer says the Tarsus IV incident occurred Stardate 2794.7. In several preceding episodes with Kirk in command the stardate given is a smaller (and thus earlier) number then the date of the Tarsus IV massacre given here, which doesn't make sense.
When Spock talks about his ancestors, McCoy comments that they were "conquered." Not only does Spock later say (in "The Immunity Syndrome") that Vulcans have never been conquered, but we've never heard anything in Star Trek or its sequels mentioning Vulcan's "conquest." And yet Spock doesn't mention that McCoy is in error - something he never refuses the opportunity to do.
If the computer has photographs and voiceprints of Kodos, why does the prosecution need eyewitnesses to identify Kodos and bring him to justice?
There were 4,000 colonists who survived the Tarsus IV execution of the other 4,000 colonists. How were there only nine people who could identify Kodos, given he was the governor of the colony?
When Dr. McCoy checked on Lt. Riley the medical scanner was on the setting for a person but it should have been off because Riley wasn't there.
McCoy: When the man on top walks along his street, the chain of command is often a noose.
Spock: Spare me your philosophical metaphors, Doctor.
McCoy: What if you decide he is Kodos? What then? Do you play God, carry his head through the corridors in triumph? That won't bring back the dead, Jim.
Kirk: No. But they may rest easier.
Karidian: Did you get everything you... wanted, Captain Kirk?
Kirk: If I had gotten... everything I wanted... you might not walk out of this room alive.
Lenore: There is no mercy in you.
Kirk: If he is Kodos, then I've shown him more mercy than he deserves. And if he isn't... then we'll let you off at Benecia, and no harm done.
Lenore: Captain Kirk. Who are you to say what harm was done?
Kirk: Who do I have to be?
Kirk: You'll never get off the ship.
Lenore: Then it will become a floating tomb, drifting through space with the soul of the great Karidian giving performances at every star he touches.
Lenore: Star light, star bright. I wish I may, I wish I might. Do you remember that, Captain?
Kirk: It's very old.
Lenore: Almost as old as the stars themselves.
McCoy: This is the first time in a week I've had time for a drop. Would you care for a drink, Mr. Spock?
Spock: My father's race was spared the dubious benefits of alcohol.
McCoy: Oh. Now I know why they were conquered. What are you worried about? Jim generally knows what he's doing.
Spock: It was illogical for him to bring those players aboard.
McCoy: Illogical? Did you get a look at that Juliet? That's a pretty exciting creature. Of course your, uh, personal chemistry would prevent you from seeing that. Did it ever occur to you that he might like the girl?
Spock: It occurred. I dismissed it.
McCoy: You would.
McCoy: In the long history of medicine no doctor has ever caught the first few minutes of a play.
Lenore: (to Kirk) All this power, surging and throbbing, yet under control. Are you like that, Captain?
Spock: Even in this corner of the galaxy, Captain, two plus two equals four. Almost certainly, an attempt will be made to kill you.
Kirk: Worlds may change, galaxies disintegrate -- but a woman is always a woman.
To further enhance the Hamlet theme of the episode, additional footage with references to that play were shot, including scenes of an inter-galactic alien entity that roamed the corridors of the ship as an allusion to the ghost of Hamlet's father. Due to the already-long running time of the episode, these scenes were cut from the final print.
This is the only episode of original Star Trek where the Enterprise's observation deck is seen.
Features recycled Mojave matte painting from "The Cage," this time it's used for Planet Q.
Originally, Bruce Hyde was cast for this episode as a character named "Lt. Robert Daikan." Only after his casting did someone remember he had played Kevin Riley in "The Naked Time" and had the part rewritten. This is the second and last time the character appears.
The music played during Dr. Leighton's get-together is a cocktail remix of Alexander Courage's Star Trek theme.
The ship's theater is a recycle of the Engine Room.
This is the final appearance of Grace Lee Whitney in production order as Janice Rand until the 1979 Star Trek movie.
Referencing a line in Shakespeare's Hamlet: "The play's the thing wherein I'll catch the conscience of the king." (Act 2, Scene ). This is the play the Karidian players perform for the Enterprise crew, and at the same time subtle foreshadowing of the final scenes of the episode, between Karidian and his daughter.