Duddle bases his drawings meticulously on Rowling’s details. He didn’t start work on each cover until he had read the book, and then would watch the film afterwards for another perspective. For certain details, such as which hand characters hold their wand in, he would check with one of the “Bloomsbury Boffins” – those at the publisher who know the intricacies of the Hogwarts world so well they didn’t need to check back through the books. Some of the questions, he suspects, were answered by Rowling herself.