The Cat in the Hat circumstances" which is soon enhanced by make believe. The book starts in a factual, realistic world, which crosses over into the world of make believe with the loud bump that heralds the arrival of the Cat. However, this is the first Dr. Seuss book in which the fantasy characters, i.e. the Cat and his companions, are not products of the children's imagination. It also differs from previous books in that Sally and her brother actively participate in the fantasy world; they also have a changed opinion of the Cat and his world by the story's end. Ruth MacDonald asserts, ""The
The Cat in the Hat for the series, including "The Cat in the Hat Comes Back" (1958), "Green Eggs and Ham" (1960), "Hop on Pop" (1963), and "Fox in Socks" (1965). He initially used word lists of limited vocabularies to create these books, as he had with "The Cat in the Hat", but moved away from the lists as he came to believe "that a child could learn any amount of words if fed them slowly and if the books were amply illustrated". Other authors also contributed notable books to the series, including "A Fly Went By" (1958), "Sam and the Firefly" (1958), "Go, Dog.