"Where No Man Has Gone Before" (unaired pilot version from TOS Season 3 BD box set). In this version Mitchell's line near the beginning of the show "Kelso's voice seemed a little nervous there" [or words to that effect] makes more sense. Also Kirk's line to Spock "Terrible having bad blood like that" adds "But you may learn to enjoy it someday". Why in the world was that excised from the aired version? Surely the censors couldn't have objected to that.