The crossword that appears in the episode featured in The Guardian newspaper and all the questions were written by Steve Pemberton himself.
Writer Steve Pemberton says the fact that the female character is called Nina, and there are references to Checkhov's play The Seagull whose lead character is Nina, is a coincidence. The reason she is called Nina is because that is a slang term for hidden references in a cryptic crossword.
Filmed in the same gothic house as The Harrowing, Seance Time, Psychoville and Whitechapel.
The sound of Nina's head hitting the floor is real. Reece Shearsmith pushed Alexandra Roach a bit too forcefully during the take, resulting in her head hitting the hardwood floor. The actual sound of Roach's head hitting the floor was used in the final cut.