When they first receive the signal, Kirk orders it broadcast over the ship's systems, as is clear because there are shots of everyone else listening. But... why? There's no reason everyone on the ship needs to hear it and there's no indication the ship somehow forces people to rebroadcast it.
Held at phaser point by Uhura, Dara asks the computer for the location of the hiding Enterprise officers...and gets the answer. So...why didn't Dara just ask the computer earlier while she and her followers were doing a search for them and couldn't find them?
As Nurse Chapel opens the door to the room where Spock is, the left arm of her uniform is red instead of blue.
Nurse Chapel is wearing a red uniform when she beams down, but a blue uniform in all prior and subsequent shots.
This planet has the same name (Taurus II) as the barren planet Taurus II in the original Trek episode "The Galileo Seven." Since this planet is being explored for the first time in this episode, it can't be the same planet.
Spock: The form is humanoid. There are many internal differences. Their bodies appear to function on an unusual psychokinesis level.
McCoy: First time I ever admired a body function.
This episode along with "The Survivor" was released on The Animated Adventures of Gene Roddenberry's Star Trek: Volume 3 for VHS.
Writer Margaret Armen previously wrote original Trek episodes "The Cloudminders," "The Paradise Syndrome," and "The Gamesters of Triskelion." She will go on to write "The Ambergris Element" later this season.
Although not canon, this episode is technically the first time that Uhura assumes command of the ship.
The first of several times that the crew (and writers) use the transporter buffer as a convenient way to "fix" some strange condition besetting the crew. This tradition goes on into the Next Gen episodes and beyond. In fact, a very similar method was used to restore an aged Dr. Pulaski to health in "Unnatural Selection".
Lorelei was the name of a woman who, according to legend, was transformed into a siren after her death. Her singing hypnotized those who heard it, drawing helpless sailors to their deaths.