A companion to last year's Lots of Rot, with the same mix of statement and see-for-yourself experiment. First, on the nature and function of fuzz, we learn that frogs, fish, and snakes, all cold-blooded animals, are bald; but warm-blooded ones need fuzzy stuff--hair, fur, down, or wool--for insulation and protection. In plants, it serves as umbrellas for flying seeds or as tiny pipes for transporting nutrients. All this fuzz, says Cobb, is made of fibers (she notes that people now make artificial fibers too), which she has readers investigate in different ways as the lesson proceeds--hand-twisting lambs' wool into yarn, or (a project borrowed from her recent Secret Life of School Supplies) making their own paper from clothes-drier lint. But will kids consider it worth the trouble of getting fibers from a pineapple leaf to obtain the ""slimy, smelly stuff"" they're warned they'll end up with? And do parents really want the kids pulling threads from silk scarves for a closer look at the fibers obtained from worms? Whether the learning is worth all the doing probably depends on the young readers' inclinations. The less ambitious (or less easily programmed) can always skip the projects.