The Terratin Incident
Answering a distress signal puts the ship's crew in danger as they all begin to shrink. How to save a dying race when you can't reach the controls?
This is one of the best animated episodes. The phenomenon could not be presented in live action at this time, or at least not much more convincingly than in '50s horror movies. The scientific explanations are thoughtful, and the right amount of time is spent confronting the problem: it is neither laboured nor rushed. The Terratin city reminds us slightly of Superman's Kandor, but the humour is closer to Honey, I Shrunk the Kids, released a decade later. Apparently the uniforms are made of algae-based xenulon that also shrinks, thus solving the old problem of why clothes change size with humans. (The stuff rips easily, if it's the same material in TOS.) Nurse Chapel seems unusually bright: even her fall into the fish tank is not a waste of time, since she has the equipment. The other characters make due with their new environment, though there is not much interaction. Kirk seems contradictory, going out of his way to find the Terratins, and then hesitating to save them. But he does.
Spock Saves the Day: He warns Kirk not to get close to the X-rays (but the captain does), then makes various computations of the rate of shrinking.
Oops: Spock doesn't do much here, good or bad.
Developments: The quote "I have never slumped in my life" says a lot, especially in the tone. Spock wonders why Kirk would even ask this of his perfect-postured first officer, but the shrinking makes it clear.