When Sarek tells Spock about his one face-to-face encounter with a Freelan, he mentions that the face he saw greatly resembled his own. Spock then describes his own first glimpse of a Romulan, which took place during the episode "Balance of Terror." He mentions that the Romulan Commander encountered by the "Enterprise" also strongly resembled Sarek. This is something of an inside joke, referring to the fact that the role of the Romulan Commander in "Balance of Terror" and the role of Sarek were both played by the actor Mark Lenard.