What makes the bluegreen spots on lemon peels, the shiny bumps on old potato slices, the smelly specks on damp dirty socks? Mold, bacteria, and mildew respectively, explains Cobb, in this very simple introduction that capitalizes on kids' natural attraction to ""yuk"" (who can resist the title?) and turns it into scientific curiosity. Cobb suggests some simple experiments with food and socks and other materials, along with some poking about in the woods to find ""completely rotten stuff."" She shows rot to be ""part, of the circle of living things"" and emphasizes that only living or once-living material is biodegradable and thus subject to rot--but then, without clearing up or even recognizing possible confusion, lists plastics among the ""favorite food"" of mildew. Some explanation seems called for, but otherwise Cobb does a good job with a great idea. Cartoon-illustrated with the requisite zip but little individuality.