In one scene Spock, overhears a conversation between Lokai, Sulu, and Chekov in the rec room. But Chekov wasn't seen in the room as earlier in that scene, it was Sulu and three other crewmen.
Spock rather awkwardly says, "Captain, Cheron lies between 4-0-3 mark 7 and mark 9.." In other words... 4-0-3 mark 8. Why doesn't he just say that?
When Bele's ship approaches the Enterprise and Sulu says "Brace yourselves!", Hadley is at the navigator's position despite the fact Chekov is at the position before and after. This same shot occurs when the ship approaches the planet Cheron.
Budget considerations aside, what's the point of an invisible ship if it can be readily picked up on sensors?
Trivia: The registration number of the shuttlecraft in the remastered version is SB4-0314/2, with Starbase 4 marked underneath as well as in its front.
All shuttlecraft look alike, including the one seen here. So Sulu saying, "It looks like the one stolen from Starbase 4 two weeks ago" is meaningless.
After the whole ordeal of Bele trying to take over the ship and Capt. Kirk coming five seconds from destroying the Enterprise via the self-destruct mechanism, he tells the Bele and Lokai, "I could put you in the brig for this, but I won't because you're new to this part of the galaxy..." What? Bele just tried to take over the ship and Kirk almost blew it up as a result and he's just going to forget about the whole thing and let these two people roam the ship freely? That would be like two people trying to hijack an airplane and then let go afterwards just because they are new to this country. This is quite a serious lapse in ship security and Kirk is pretty much responsible for anything that happens as a result.
At the beginning of this episode, the shuttle bay was green when Lokai fell on the floor.
When Lokai starts running, in the first close-up you can see a rope in his hand - presumably Lou Antonio and the cameraman are both holding the rope so Antonio can judge how fast to run and keep up with the moving cameraman.
Spock walks by the crewmen's lounge as Lokai gives a speech and notices the alien through the partially-opened door. Since when do the automatic doors on the ship stay partially open?
In "By Any Other Name" Kirk was reluctant to self-destruct the Enterprise even though the invaders were going to conquer the Milky Way galaxy. In this episode he cheerfully prepares to blow up the ship just because Bele wants to borrow it for a day or two to return a prisoner.
Spock tracks the two aliens running through the ship, but fails to notice them enter the transporter room - it's Uhura who finally notices they've activated the transporter from her position.
As they run through the ship, Spock says Bele passes rec room 3. We see Lokai run past the rec room. Then Spock says they've both moved to deck 5, and then he calls out "passing rec room 3" again.
Kirk gives logs using first stardate 5730.7, and then later 5730.6.
Kirk says Cheron is in an uncharted region of the galaxy. Ummm, how does Kirk know about it then? Later Spock identifies its exact position when he says the ship is heading for it. Again, if it's "uncharted" how do they know where it is to figure out this stuff.
The stolen shuttlecraft from Starbase 4 bears the Enterprise registry number. (This is corrected in the re-mastered 2008 version.)
Lokai: I am not a thief.
Kirk: Well, certainly no ordinary thief, considering what it is you... appropriated.
Lokai: You're being very loose with your accusations, and drawing conclusions without any facts.
Kirk: You can try those technical evasions on Starfleet Command. That's where you'll be facing your charges.
Lokai: I'm grateful for your rescue.
Kirk: Don't mention it. We're pleased to have caught you.
Spock: Fascinating. Two irrevocably hostile humanoids.
Scotty: Disgusting is what I call them.
Spock: That description is not scientifically accurate.
Scotty: Mr. Spock, the word "disgusting" describes exactly what I feel about those two.
Kirk: That's enough for today. Those two are beginning to affect you.
Lokai: So this is justice after Ariannus! You have signed my death warrant. I warned you what to expect. Will you continue to let this mockery of justice go on? If you are partisans of justice, prove it! Kill him!
Chekov: We are not killers.
Lokai: What do you do, carry justice on your tongues? You will beg for it, but you won't fight or die for it.
Kirk: After so many years of leading the fight, you seem very much alive.
Spock: I doubt that the same can be said for many of his followers.
McCoy: I've never worked on anyone or anything like him.
Spock: Yet, you are pumping him full of your noxious potions as if he were a human.
McCoy: When in doubt, the book prevails, Mr. Spock!
Uhura: It doesn't make any sense.
Spock: To expect sense from two mentalities of such extreme viewpoints is not logical.
Sulu: But their planet's dead. Does it matter now which one's right?
Spock: Not to Lokai and Bele. All that matters to them is their hate.
Uhura: Do you suppose that's all they ever had, sir?
Kirk: No. But that's all they have left.
Lokai: You monocolored humans are all alike! First condemn and then attack!
Sulu: No one knows how he'll act under pressure.
Lokai: You're from the planet Earth. There is no persecution on your planet?
Chekov: There was persecution on Earth once; I remember reading about it in my history class.
Spock: The actual theory is that all life forms evolved from the lower levels to the more advanced stages.
Spock: Change is the essential process of all existence.
Bele: You've combed the galaxy and all you've come up with is mono-colored trash, bleeding hearts and do-gooders. You're dead, you half-white.
Lokai: (to the crew) You useless piles of bland flesh.
Scotty: And at warp 10 that's going nowhere mighty fast.
In the original version, shuttlecraft flight through space footage is recycled from "Metamorphosis." The landing footage is recycled from "The Galileo Seven." The re-mastered 2008 version uses new footage, including a different serial number on the ship's hull.
The self-destruct sequence in this episode goes:
Kirk: Destruct sequence 1, Code 1-1-A.
Spock: Destruct sequence 2, Code 1-1-A-2-B.
Scott: Destruct sequence 3, Code 1-B-2-B-3.
After verified and engaged by the main computer, it awaits the final code for 30 second countdown, which is provided by Kirk as Code 0-0-0-Destruct-0.
The self-destruct code would eventually be reused in Star Trek III: The Search for Spock by Kirk, Scotty, and Chekov to destroy the Enterprise to prevent Klingon capture.
The story for this episode was written by Gene L. Coon under the pseudonymn Lee Cronin.