The big blue canvas reads as a burst of energy. Five figures, a green mound, a flat blue sky, almost no detail, the whole thing apparently thrown down in an afternoon. Visitors treat it that way. They stand back, take the picture, and move on with the impression that Matisse was a man who worked fast and got lucky. Then you turn around and there are the bronze heads on the plinth, the same subject remade over and over, each one further from the last.