Entering the Harry Potter creature effects workshop at Leavesden Studios is a bit like entering Hogwarts itself: You never know what you’re going to find around each corner. Over the past decade, Nick Dudman and his team of artists and technicians have built every imaginable character from house elf to hippogriff. As a visitor soon discovers, the latest film, Harry Potter and the Half-Blood Prince, is no exception to that wide range of work.