What causes tickling? : Leonardo da Vinci -- Candles on his head : Michelangelo Buonarroti -- The uninvited guest : Peter Bruegel -- She introduced laughter : Sofonisba Anguissola -- From riches to rags : Rembrandt van Rijn -- Old man mad about drawing : Katsushika Hokusai -- Riding a tall horse : Mary Cassatt -- Risking his life for art : Vincent van Gogh -- Mountain climber, mother, and model : Kathe Kollwitz -- King of the wild beasts : Henri Matisse -- At the bullfights : Pablo Picasso -- Clowning around : Marc Chagall -- The art of chess : Marcel Duchamp -- Skulls and flowers : Georgia O'Keefe -- Handstands on the beach : William H. Johnson -- How to shock the world every twenty-four hours : Salvador Dali -- A tiger on the stairway : Isamu Noguchi -- Frog-face and the walking flower : Diego Rivera and Frida Kahlo -- Eating the entire birthday cake : Andy Warhol.