The mandolin looks harmless enough. About the size of a tennis racket, it's easy to get a clear, golden sound just by brushing your pick across its four sets of double strings. That doesn't mean I didn't feel slightly panicky when my wife surprised me with one when I hit the big '4-0. "We support you, sweetie," Ruth said, speaking for the family. By day 7n, she and our 4-year-old would quietly slip into another room whenever I took a crack at "Turkey in the Straw."