As established, when the transporter beams someone down, it immediately restores them to normal size. However, when the Mendent tells Gabler and three other unidentified crewmen that their city is close to destruction, the Enterprise crewmen are still at their miniaturized height. If they had beamed down from the Enterprise, they would be at their normal height.
When Kirk goes to the transporter room to inspect the Terratin city, the macroscope he uses is pointing at an angle toward the floor. However, when he looks through it at the Terratins, the view is if he were at ground level with them.
For some reason when Scotty is on the bridge briefing Kirk and Spock on the engines, nobody else is on the bridge. Given they're in a potentially hostile situation with time running out for them to analyze the situation and respond to it, why would the entire bridge crew leave, regardless of the shift.
Trivia: The Elysian Council appears to be made up of; Xerius (a Romulan), Devna (an Orion), a Klingon, a Kzinti-like creature but somewhat chubbier (see "Slaver Weapon"), an Andorian, an antlike creature, a plant creature (similar to the Phylosians in "The Infinite Vulcan"), an Aquan (perhaps from the planet in "The Ambergris Element"), a Vulcan, a Tellarite, a Human in an old-style Federation uniform, and a Gorn.
Kirk refers to the stardate as "52.2". Later he refers to it (correctly) as "5267.2" - they left out the "67" in the earlier reference.
The aquashuttle lands during the day. However, when Kirk calls Scotty for beam up, the sky behind him is a night sky.
When Kirk and Spock begin to explore the ruins of the old city, one shot shows Spock's uniform colored gold instead of blue.
Trivia: This episode features the only time in the series that anyone dies on-screen.
When the Slaver weapon is in "power drain" mode, why does it not drain the life support belts? It drains the police net.
When Spock first sees the miniaturized AI computer, he expresses astonishment that it's so small. But a minute or two later he says that the matter-conversion weapon is the only item the Federation doesn't already have. So which is it?
When Chuft Captain initially tests the slaver weapon, the weapon changes differ between what he holds and what he points at Sulu. At several points it reverts backwards, changing repeatedly and out of sequence from communications device to laser to telescope and back again.
Spock's life-support belt disappears in one shot.
When the trio exit the shuttlecraft through the rear exit, the doors slide into the sides...except the sides are minimally thin. There's nowhere for them to go.
In one shot, the Ariel crew have their insignia on the wrong side of their uniforms.
Lt. Cmdr. Markel has Commander stripes.
In one shot Spock has normal human eyebrows.
The Ariel crew appear to wear the same insignia as the Enterprise. During the original five-year mission, different starships had different insignia.
The perspective was very poor in the temple. When they get inside, we see the sculptured indurite floating, and Sord says, "Pretty bauble. How do we reach it?" From the angles, it looks as if all they have to do is walk across the floor and take it. Even when they scramble up on the ledge, it does not look very far off the ground, but Kirk suddenly makes the comment that it is "a thousand feet up."
The volcano sequence doesn't make much sense. The vehicle grinds to a halt and the lava is flowing just behind them. Then they go to divert the lava, which is apparently now several minutes behind them. Then after they get going the lava is again a few feet behind them, but Spock falls out and Kirk goes to get him and the lava is nowhere to be seen.
Kirk and Spock don't wear force field belts (see entry under Notes for "Beyond the Farthest Star") on the asteroid; but when inside the temple and Kirk walks to the wall, he suddenly has one on for a few moments.