I still speculate how Zetarians became glow-lights and where Kelvans got their skin-suits.
For the Zetarians, I speculate that Fred Freibeger said "Let's save some money on special effects and just shoot some film of my blinking Christmas tree lights!"
I address ST:TOS aliens in one section of my blog:
. She is a highly intelligent and accomplished woman to be sure, but she is also emotionally distant, cold and not very friendly. (Thank heavens Spock and Scotty have some sense, and finally McCoy begins to see through her!). Marvick must thrive on rejection, I guess....

