Episode Behind the Scenes

Walter Koenig was allowed to write this episode after having been left out of the main cast due to budget constraints.
Walter Koenig became the first "Star Trek" actor to write an episode. Other actors such as Robert Picardo and Brent Spiner would go on to follow in Koenig's footsteps.
As an in-joke, Walter Koenig wrote the line for Captain Kirk: "We always encourage our officers to make friends with the natives." Ensign Pavel Chekov said the same thing to Captain Kirk in the classic episode "Spectre of the Gun." Another in-joke; the name of the plant that poisons Sulu, "Retlaw", is "Walter" spelled backwards.
Though the common phrase associated with "Star Trek" is "Beam me up, Scotty", the line was never said in any of the 79 original episodes or any of the 22 episodes of "The Animated Series." However, its closest variation is said in this episode, as well as in "The Lorelei Signal", in the form of "Beam us up, Scotty."
In somewhat of a prelude to "Star Trek II: The Wrath of Khan", Mr. Spock's katra, though unnamed in this episode, simply referred to as his mind, is transferred to his giant clone. It is restored by a mind meld, similar to the ending of "Star Trek III: The Search For Spock."
First instance of a crewmember being cloned. Several others would experience a similar procedure, such as Captain Picard in "Star Trek Nemesis", and Commander Riker and Dr. Pulaski in "Up the Long Ladder." However, out of all four, only Mr. Spock's clone continues to live on. Ensign Travis Mayweather from "Star Trek: Enterprise" was also cloned in the episode "Dead Stop", however, that clone never lived in the first place.
Keniclius references the Eugenics Wars first introduced in the classic episode "Space Seed."