Actor Kevin McCarthy occasionally cited his performance in this episode - playing a character who was immortal - as seemingly having come true in his own life, as he remained in good health and continued to act while outliving most of his family and colleagues as he approached the age of 100. McCarthy died September 11, 2010 at the age of 96, having earned an acting credit as late as the year he died, more than 50 years after this episode was produced.
The trivia item below may give away important plot points.
Kevin McCarthy's transformation from a middle-aged to an old man on-screen - without any cutaways - was accomplished by applying red-colored age makeup to McCarthy's face and then lighting the set with red key lights, which disguised the age makeup. As the scene progressed, the red key lights were gradually replaced with green lighting, a change imperceptible to the black-and-white film in which the scene was shot, but which made McCarthy's face appear to age spontaneously - something that normally couldn't be done with early 1960s technology without taking the camera off the actor for at least a brief cutaway.