Episode Behind the Scenes


First appearance of Mr. Spock's parents, Sarek and Amanda, played by Mark Lenard and Jane Wyatt, respectively. Lenard would reprise the role in "Yesteryear" on "Star Trek: The Animated Series", as well as in "Star Trek III: The Search For Spock", "Star Trek IV: The Voyage Home",  "Star Trek VI: The Undiscovered Country", and two episodes of "Star Trek: The Next Generation"; "Sarek" and "Unification, Part I". (Sarek would also appear in "Star Trek V: The Final Frontier", although he'd be played by Jonathan Simpson.) Although Amanda also appeared in "Yesteryear", she was voiced by Majel Barrett. Wyatt would reprise the role in "Star Trek IV: The Voyage Home".
When Thelev attacks Kirk in the corridor, listen carefully to the sound of them fighting and you will hear a totally out of place sound that sounds something like a bongo drum being hit or the sound a cartoon might make when a coconut falls on someone's head. A sort of hollow percussion sound that's totally out of place.
The assassin politely takes time out to adjust his tunic, giving Kirk time to recover from his attack. Then he stabs at Kirk with his knife in his left hand - there's a camera cut to Kirk kicking him and the knife has jumped instantaneously to his right hand.
When Sarek goes into the reception room to take his pill, the Tellarite holding the drink has it in his left/right/left hand depending on the camera shot.
In one scene on the bridge, the space sensor array was not moving.
In one scene the Enterprise's phasers were pink instead of blue.