 After defeating the head Sycorax in the sword fight, the Doctor  makes a comment about his outfit being very "Arthur Dent" and going  on a short bit about what kind of person he was (just prior to  discovering the fruit in his robes pocket). This is a reference to  "The Hitchhikers Guide to the Galaxy". Douglas Adams, the creator  of the story, was a writer for the "Doctor Who" series.