Take the letter D, for instance. Turn it to one side and it's a laughing mouth, to the other and it's a frog's eye. Upside-down, it's a teacup handle. Or take Q. On its side, it's a magnifying glass or a tag on a dog's collar; upside-down it's a pendulum on a clock. This is hands-on entertainment (and education) in which part of the pleasure is physically rotating the book to follow each letter's permutations. For adults, Ernst's geometric designs and striking hues may evoke the color-field experiments of artist Josef Albers. Kids will be more interested in the way an upside-down A becomes a drippy ice-cream cone or a sideways E turns into an electric plug. Ernst's ingenuity is equal even to the challenge of letters that don't change when turned, like O (a bagel, an owl's eye, a fried egg) and X (a railroad-crossing sign, a treasure map's end, a ballerina's shoe ribbons).