From "Requiem For Methuselah"
29 minutes into the episode:
SPOCK (on monitor): Most interesting. Our host appears to wish us to linger, yet he is apprehensive. [Start Cue] It is logical to assume that we are being monitored and that he is aware of our every move.
(Flint turns off the monitor)
RAYNA: You sent the [Cue ends] robot to kill him.
*Of interest in this episode is that the music preceding the cue is from the first part Track 18 of Spock's Brain.