filming Star Trek - deleted recreation room scene another frame from the deleted recreation room scene from the third season episode “Elaan of Troyius.” filmed June 10, 1968 (via)

Oh yeah…

This is where Kirk asks Spock to play a song, and Spock says “okay” before starting to play a Vulcan love song.

Literally the face Kirk makes when Spock agrees to play a love/mating song, explains that the lyre was used in ancient times to "stimulate the fury" of mating, and Kirk replies, "We'll need some stimulation--very fast" :

And then once Kirk leaves and the other three are staring after him, McCoy tells Spock, "If you're going to serenade that one, you'd better put some real emotion into it." [emphasis mine 😘 I mean of course he was talking about Elaan, not Kirk...]