She's a Mona Lisa, familiar yet unreadable. Is that smile playing across her lips pleasure at her overnight fame or amusement at the paparazzi falling over one another in their eagerness to snap her? A slinky bridesmaid's dress at the wedding of her sister Catherine, Duchess of Cambridge, thrust Pippa backward into the public eye. One picture editor says he is offered as many as 400 images of her a day. She's now reputed to have a book deal, which may be a mistake. Mona Lisa never speaks.