Trivia: Producer William Froug rejected an extremely nervous young singer/actress auditioning for the part of Mary Rachel, and recalls thinking that "I'll probably kick myself. She'll probably be a big star." He turned out to be right on both counts. The aspiring young singer's name was Liza Minnelli.
Trivia: Rod Serling set up a practical joke on writer Richard Matheson when the two were flying to San Francisco aboard a propeller-driven plane. Serling collaborated with the airline to tape a poster blow-up of the "Nightmare" gremlin's ugly face to the outside of the plane window. Just as Serling prompted Matheson to open the curtain, however, the plane's engines and props fired up, blowing away both the poster and Serling's intended gag.
Trivia: Uncle Simon's mechanical man is a thinly-disguised Robby the Robot from Forbidden Planet, with a different head and "face" under his glass dome. Robby guest-stars with his original head a few Twilight Zone episodes later, in "The Brain Center at Whipple's." (00:17:00)
Trivia: Writer Richard Matheson says he was pleased with most of Twilight Zone's film version of his short story - except for the gremlin. He'd conceived it as a dark, creepy and nearly-invisible humanoid figure. "But this thing," he complains, "looked more like a panda bear."