This is the only episode in which Uhura and Sulu call Scotty by his nickname. Otherwise, they call him "Mr. Scott."
For his first four appearances in the series, including this episode, Walter Koenig wore a The Monkees (1965)-style wig, which he absolutely detested. In one interview, he made joking and uncomplimentary references to that wig.
The actors playing Capellan warriors were given elevated shoes to make them appear like giants. Maab's high headgear served the same purpose. This was also addressed in the mission briefing on the Enterprise by Dr. McCoy who said it's not unusual for the locals to be 7 ft tall.
Third time Bones uses the saying "I'm a doctor, not a ..." (In this case, escalator.)
This is the first episode where all seven "classic" crew members (Kirk, Spock, McCoy, Scotty, Uhura, Sulu, and Chekov) appear in the same scene, in the teaser, discussing the background for the Capellans, although Sulu is seen only on a view screen reporting from the bridge. The other six are all in the same briefing room together. The six also appear in the same scene together at the very end on the bridge, but Sulu is still absent, although the right arm of a helmsman that should be him is seen at the right edge of the screen.