In such books, words are a kind of 'language play' which enables the child listener/ 'looker' - these books are designed on the assumption that an adult will be reading along - to anticipate and then relish the explosive humorous moment which is also captured in the illustrations. The most popular tools for authors creating this kind of 'language play' are rhyme and repetition, both of which engender laughs with the least effort while also providing the best platform for pre-speech participation, as the very youngest listeners can make matching sounds even if they can't repeat the whole word.