Book excerpt: If it were possible to shrink down and take a tour of a human body, would you want to go? Readers will get that chance when they explore the body of a guy named Marty, who will let them check out the body systems that keep his heart beating and his body moving every day. With the help of a tiny ship that goes through his ears and all the way through his digestive system, readers will learn exactly what they are made of with this great book.