** After the end of the movie, you realize that [[spoiler:The Girl is the Devil and has chosen Corso for the gift of the power since the beginning.]]
** Alternate interpretation: [[spoiler: Corso is actually Satan and has undergone a MemoryGambit to return to heaven. The book is supposed to "raise the devil" and so it does, by showing him the way back home.]]
*** [[spoiler: Not only that, but when Balkan tries to summon the Devil, who appears but Corso, who even says "I'm the only devil you'll see tonight." Sure, Balkan's plan was flawed due to the forgery of the ninth engraving, but the symbolism is there.]]
** In the book [[spoiler: The Girl/Irene Adler is not the Devil, but still a fallen angel, and Corso is a normal human haunted by tragedy in his life and his ancestor's. In the film, either character can be seen as the Devil. Kind of like how the three books each hold some answers.]]
** There's another possible interpretation of the film (though not necessarily the book), in that [[spoiler: the Ninth Gate really had nothing to do with Satan. According to this theory, the "Lucifer" referred to as the author of the Delomelanicon referred to the name's literal translation of "Lightbringer," and not the demon of Christian mythology. The engravings serve as a map of consciousness, not unlike the Kabbalah, and lead down two separate paths, one a path of greed and self destruction which ends in flames, and the other, a true path to enlightenment. Aristide Torchia (and by extension, all those who interpret the material as Satanic) follows the negative path and dies as a result. Dean Corso somehow ends up on the right path, and achieves transcendence.]] A much more detailed explanation can be found [[http://www.halexandria.org/dward900.htm here]]
* FridgeLogic: Considering Corso and the other characters are all experts on rare books, why does Corso never wear any sort of hand protection when examining them and is allowed to drink and smoke near them? The Baroness is the only one who seems to be annoyed by such behavior, rightfully so.
** The books being laid out on the floor in Fargas' mansion was actually taken from the source novel. Not that it necessarily makes it better....
** Books prior to the invention of the printing press were printed on extremely heavy paper or vellum, not mere pulp, with bone spines (hence the name "spine") and leather covers; don't think "rare pulp magazine", think ''"man-portable stone tablet"'' - something sturdy to preserve knowledge for the ages. Antiquities dealers treat them with care because they're valuable, not because they're delicate. Back when they were first written, readers smoking and drinking near them was basically [[ButForMeItWasTuesday Tuesday]] - people read them by candlelight, and if you didn't drink liquor you were drinking (not-so)CoolClearWater. Still doesn't excuse a "rare book dealer" being so rough with them though.
*** TruthInTelevision: Real old books are commonly handled without any gloves (though smoking and drinking around them are definitely not allowed), because wearing gloves leads to loss of tactile function, which could actually lead to inadvertently tearing pages or damaging the book. Furthermore, if a book happens to get damaged, it's often repairable.
* FridgeLogic: The Girl saving Corso from his attackers and with such questionable and possibly inhuman fighting skills. And TheReveal where she descends... Still remember that. I liked it was subtle. Just kinda slipped in there. To the point where the audience questioned their own eyes. “Did she fly or just slide down the railing?"