PUF!, PIU! and CRACK! are the titles of a non-fiction books series for very young children. With their small, quadratic format, made of sturdy cardboard, and featuring a simple, robust pop-up mechanism, these books are very well-suited to be manipulated repeatedly, to be opened, read and looked at. PUF! is dedicated to the topic of poop, PIU! to the topic of feathers and CRACK! to the topic of eggs. The cheerful, funny pictures contribute to the playful, relaxed character of this book.