About 50 rapt children and their parents were a standing-room-only audience Saturday at the Glen Park Library, when lion dancers from the Jing Mo Athletic Association gave a demonstration of the decidedly athletic art of being a lion. Kids got an inside peak into how a lion costume works and even got to ‘feed’ it a ceremonial head of lettuce. The event, sponsored by the Friends of the San Francisco Public Library, celebrates the coming of the Lunar New Year — Year of the Tiger, 4707.