 The episode was partly inspired by H. G. Wells' 1904 novel "The Food of the Gods and How It Came to Earth" and its theme of animal size change.Another influence was the 1927 film "The Cat and the Canary" and its 1939 re-make, both of which feature haunted house premises and stalker characters.Writer Alan Pattillo, who according to special effects supervisor Derek Meddings "had tried to come up with the most nightmarish rescue situation he could", had wanted to direct the episode as well.