- Development Gag: Kirk's joke at the end that Spock looks like Satan is a deliberate reference to fears from NBC that viewers would think Spock was Satan and complain. NBC even attempted to hide Spock's ears in early promotional material before Spock quickly became a Breakout Character.
- Like a Duck Takes to Water: Kirk isn't too concerned about the newly liberated Vaalians as far as how they will now reproduce. Apparently "sex" needs no instruction manual anywhere in the galaxy.Kirk: Ahhhh... Just keep doing what you're doing and you'll find out... eventually.
- Prop Recycling: Celeste Yarnall wore Grace Lee Whitney's costume, left over from season one. It was recut and fitted to suit her. Worrying if Whitney might return and need the costume, Bill Theiss assured her that she will never return.
- What Could Have Been: This episode's original script called for an emergency saucer separation. However, due to budgeting, the effect was only mentioned but not seen. It was seen for the first time in Star Trek: The Next Generation's debut, "Encounter at Farpoint".
Trivia / Star Trek S2 E5 "The Apple"