Your birthday-suit is made of pretty smart material. True, over time, its crease-resistance may fail to satisfy (a billion-dollar cosmetics industry is working on that) but this remarkable organ serves the wearer well (page 8). In 1911, a nine-year-old girl wrote a letter to Father Christmas. She posted it up the chimney... and there it waited 85 years to be read. This true story is the inspiration behind this week's poster, which will set young writers thinking. Did Mabel ever get her sweets? Did Santa 'remember the very poor children in the slums'?