What is the meaning of the proverb"still waters run deep"

Match the artists with his technique or to his work. 1 . michelangelo the illusion of depth 2 . giotto perspective and chiaroscuro 3 . raphael "the last supper" 4 . velazquez "sistine madonna" 5 . holbein "david" 6 . masaccio portrait of henry viii 7 . van eyck flemish painter 8 . da vinci spanish painter