As Soucie explains in this entry to the What's the Difference series, monkeys have tails and apes don't. Forty similar questions about plants and animals are answered in this slim, attractive book handy for nature browsing. Each spread poses a question and provides clues to the answer with accompanying black-and-white line drawings and boxes of odd, interesting facts. It's too bad that the author does not provide the sources for his answers; sometimes he presents a scientific definition (e.g., distinguishing between fruits and berries) and other times the answer is based on common usage (weeds and grasses). Children will enjoy puzzling over hares and rabbits, molds and mildews, newts and salamanders, and many other intriguing pairs.