Book excerpt: Sides (contributing editor, Outside) fields questions from readers of his column "The Wild File." Focusing on natural history and outdoor lore, this collection includes questions about the strange doings of the natural world. Do beavers ever get squashed by the trees they're chewing down? What good are goosebumps? Why do men have nipples? How do penguins keep their feet from freezing? Why do llamas spit? c. Book News Inc.