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Rattlebacks are stones (in this case, carefully made plastic reproductions) with a surprising property: they only spin one way. Try as hard as you can, spin as hard or as gentle as you can, you'll find that it will actually change direction and spin the one way it likes. Seems to violate the laws of physics! A great brain baffler for kids 5+. Rattlebacks can also be used as magnifiers! See if you can figure out the explanation for its spin!