When Scotty told the landing party to bend down because the ceilings were low in Balok's ship, everyone put their hands on their legs but when they arrived, Dr. McCoy's hands were not on his legs anymore.
In the very first shot in this episode of the Enterprise and the quick zoom in towards the bridge the front of the warp nacelles had short gold spikes on them and the bridge dome was slightly different.
This was due to the staff reusing footage from the beginning of the "The Cage."
Spock states that the Fesarius (Balok's ship) "must be a mile in diameter". Yet any one of the small spheres that make up the Fesarius dwarfs the Enterprise. If the Enterprise is about
300m long, the Fesarius would have to be around 6 km in diameter--considerably larger than a mile.
Lt. Uhura had a science patch on her uniform but she had a command (gold) uniform.
Sulu said that the cube's angles each measure 107 meters, the Enterprise is 289 meters long, if the cube
was 107 meters in size, it would have to be about 1/3 the size of the Enterprise!
Kirk calls the Enterprise the "United Earth Ship" (U.E.S.) Enterprise, he should have said "United Space Ship" (U.S.S.)
When Kirk gives his speech shipwide to the crew, in one hallway camera shot a crewman is totally frozen with one foot raised in the air.