Grades 4-6. The team that penned Poop: A Natural History of the Unmentionable (2004) presents another title with a unique twist. Illustrated with winsomely crude cartoons (think Diary of a Wimpy Kid), this small, rectangular volume packs in a ton of information on the mathematically based rule governing how big or little an animal can get while still being able to get airborne (like a fly) or walk on water (like a water strider). Using the hook of superheroes, a dose of physics is made simple. For example: humans can’t ever race across walls like a gecko because every time an animal doubles size, its weight and volume increase eight times. A person, therefore, would need ridiculously big, long toes—all out of proportion to what a gecko is equipped with—to keep off the floor. A glossary and index are included, making this useful for reports; but future biologists will probably enjoy perusing this book just for the pleasure of understanding principles about the animal world not easily found elsewhere.