While he was a boy, says Vasari, Lionardo modelled in terra-cotta certain heads of women smiling. This was in the workshop of Verocchio, who had already fixed a smile on David's face in bronze. When an old man, he left "Mona Lisa" on the easel not quite finished, the portrait of a subtle, shadowy, uncertain smile. This smile, this enigmatic revelation of a movement in the soul, this seductive ripple on the surface of the human personality, was to Lionardo a symbol of the secret of the world, an image of the universal mystery. It haunted him all through his life, and innumerable were the attempts he made to render by external form the magic of this fugitive and evanescent charm. Through long days he would follow up and down the streets of Florence or of Milan beautiful unknown faces, learning them by heart, interpreting their changes of expression, reading the thoughts through the features. These he afterwards committed to paper. We possess many such sketches--a series of ideal portraits, containing each an unsolved riddle that the master read; a procession of shadows, cast by reality, that, entering the camera lucida of the artist's brain, gained new and spiritual quality.[239] In some of them his fancy seems to be imprisoned in the labyrinths of hair; in others the eyes deep with feeling or hard with gemlike brilliancy have caught it, or the lips that tell and hide so much, or the nostrils quivering with momentary emotion. Beauty, inexpressive of inner meaning, must, we conceive, have had but slight attraction for him. We do not find that he drew "a fair naked body" for the sake of its carnal charm; his hasty studies of the nude are often faulty, mere memoranda of attitude and gesture. The human form was interesting to him either scientifically or else as an index to the soul. Yet he felt the influence of personal loveliness His favourite pupil Salaino was a youth "of singular grace, with curled and waving hair, a feature of personal beauty by which Lionardo was always greatly pleased." Hair, the most mysterious of human things, the most manifold in form and hue, snakelike in its subtlety for the entanglement of souls, had naturally supreme attractiveness for the magician of the arts. With like energy Lionardo bent himself to divine the import of ugliness. Whole pages of his sketch-book are filled with squalid heads of shrivelled crones and ghastly old men--with idiots, goîtred cretins, criminals, and clowns. It was not that he loved the horrible for its own sake; but he was determined to seize character, to command the gamut of human physiognomy from ideal beauty down to forms bestialised by vice and disease. The story related by Giraldi concerning the head of Judas in the "Cenacolo" at Milan, sufficiently illustrates the method of Lionardo in creating types and the utility of such caricatures as his notebooks contain.[240]