Sources: - The Encyclopaedia Brittanica entry on Film Noir

- Esquire articles written by Olivia Ovenden:

* https://www.esquire.com/uk/culture/film/a38816679/nightmare-alley-ending-explained-by-guillermo-del-toro/

* https://www.esquire.com/uk/culture/film/a38811871/guillermo-del-toro-favorite-movies-noir-nightmare-alley/

- Article by PATRICK BRZESKI:

* https://www.hollywoodreporter.com/movies/movie-features/making-of-nightmare-alley-gullermo-del-toro-1235073035/