"The Phantom Tollbooth" contains allusions to many works, including those loved by Juster in his own upbringing. Some of Juster's favorite books as a child, including "The Wind in the Willows", had endpaper maps; Juster insisted on one, over Feiffer's opposition, going so far as to sketch one and require that his collaborator reproduce it in his own style. Juster was also inspired by his father Samuel's love of puns, with which the book is more than sprinkled. In his childhood, Juster spent much time listening to the radio. According to Juster, the need to envision the action when listening to radio serials helped inspire "The Phantom Tollbooth", as well as yielding the character of Tock, based on sidekick Jim Fairfield from "Jack Armstrong, the All-American Boy". Jim gave Tock his wisdom, courage, and adventurous spirit. As a child, Juster had synesthesia, and could only do arithmetic by making associations between numbers and colors. He remembered that the condition affected word associations. "One of the things I always did was think literally when I heard words. On the "Lone Ranger" serial they would say, 'Here come the Injuns!' and I always had an image of engines, of train engines."