There are several references to the "Harry Potter" franchise. At one point, Martha says "It's all a bit Harry Potter", which prompts the Doctor to claim that he has read the final book in the series (which would not be released until three months after the episode was aired; the Doctor refers to it as "Book 7" because the title had not been made public at the time of filming). At the end of the episode, Shakespeare, the Doctor and Martha use a word from "Harry Potter", "Expelliarmus", to defeat the Carrionites, and the Doctor exclaims "Good old J.K.!". These references include some metatheatrical humour, since David Tennant played the villain Barty Crouch, Jr in the film adaptation of "Harry Potter and the Goblet of Fire".