There's a penetrating chill in the wind. The bright moon rises behind the shivering, nearly naked trees. A profound sense of foreboding permeates the darkness. This is the night, after all, when witches ride their broomsticks through the sky, and the natural world is forced to confront the powers of the supernatural. No, it isn't October 31 and this is not Halloween. It's April 30 and it's Walpurgis Night.