Video game reference: The old-fashioned camera that Abigail uses in the film is a reference to the popular "Fatal Frame" (known as "Rei Zero" in it's native Japan, and as "Project Zero" in Europe) series of horror/survival games, upon which the "Stay Alive" concept is partially based.
Although the term "Blood Countess" is used in the movie's synopsis, it is never said within the movie. When Hutch and Abigail are hearing the story of Elizabeth Bathory from the author of the book "The Lady of Blood", the author says, "Thus began her obsession" (speaking of using the blood of the girls as a "Fountain of Youth", as Abigail says), to which Hutch replies, "The Blood Countess" (not in the theatrical version, but at approximately 1 hour 1 minute and 44 seconds on the uncut-version DVD).
The trivia item below may give away important plot points.
October, played by Sophia Bush, says, "Go fuck yourself," to her killer before she is murdered. That line is said by Neal McDonough in 2007's The Hitcher, which stars Bush. Coincidentally, McDonough says, "Go fuck yourself," to his killer before he is murdered.