Koenig asked to play the part of Dr. Keniclius. Roddenberry and Fontana approved, and the show's producers allowed him to audition, but he said later that he suspected it was "a very token gesture" and they were not seriously considering him. He included a reference to himself in the episode, as the walking plant is called a Retlaw – Walter spelled backwards. This was a reference to aliens in the 1940s comic book "Planet Comics" who spoke backwards. He later used a similar idea in "The Stranger", a "Land of the Lost" episode he wrote, in which Koenig introduced the character Enik. This character was originally called Eneg, backwards for Gene as a reference to Gene Roddenberry.