The first episode where Tony calls Jeannie "Darling" (although she wasn't there to hear it). She later says in the season 5 Never Put a Genie on a Budget (1969) that she loves it when he calls her Darling.
Newcomer and day player John Beck, who has about a minute of screen time with Larry Hagman, would later spend several seasons as a principal on Larry's series, Dallas.
In under two years, Arlene Martel goes from playing the wild and crazy cosmonaut
to the logical Vulcan (on Star Trek) who used James T. Kirk to get out of marrying Spock.
She went from unknown to immortal in the minds of every Trekkie.