Perhaps that famed trio of witches wouldn't have been so crotchety if they'd been stirring up these bubbling floats. For a dastardly presentation, set a large metal bowl inside a larger cauldron. Wearing gloves or oven mitts, place dry ice in the cauldron around the bowl, then fill the bowl with root beer. Pour water onto dry ice for a steamy effect. To serve, ladle root beer into mugs filled with scoops of gall of "goat" or vanilla ice cream.