DO PENGUINS HAVE KNEES?

``They sure do, although they are discreetly hidden underneath their feathers,'' answers Feldman in this latest addition to his best-selling ``Imponderables'' series (Why Do Clocks Run Clockwise?, etc.). ``What causes the green-tinged potato chips we sometimes find?''; ``How do they fork split English muffins''?; ``What happens to your Social Security number when you die?''— these and 141 other brain-itching questions are expertly scratched by the author in lighthearted short-take responses, usually informed by expert advice from a manufacturer, scientist, sociologist, etc. And as in previous volumes, this congenial work, as addictive as a box of bon-bons, ends with a flurry of ``Frustables''—that is, possible unanswerables, e.g., ``Why do you so often see one shoe lying on the side of the road?'' (For those who can't wait until pub date: the green in potato chips is caused by chlorophyll; English muffins are split by being passed through two spinning wheels with Roman spear forks; and when you die, your Social Security number goes with you.)