First, top a pizza crust with pizza sauce and shredded mozzarella. To make the spider, place olive half on pizza, surround with 8 thin slices to form legs. Bake the pizza according to the instructions on the crust's package. With a paring knife, trim away bits of mozzarella cheese slices to form head and arm shapes for ghosts. With 3 minutes of cooking time left, set the ghosts on the pizza, then finish cooking. Remove the pizza from the oven and add bits of olives for eyes. Serve warm.