Goof: When the numerologist, Vicki Louise Burdick (Ellen Greene) is lying dead on the examination table at 22:45, you can see her eyes moving under her closed eyelids.
As Agent Reyes gets into lift near the start of the episode there are 7 passengers with her. They line up in the lift like an 8 in a deck of cards.
Even if the universe is run by numbers, it would have nothing to do with the way we humans decided to write them, i.e., 2, 5, 8 etc.
(Mr. Burt opens the trunk of his car, which is full of CDs with a checker board placed on top)
Scully: What are those?!
Mr. Burt: CDs.
Scully: You must really like music.
Mr. Burt: Oh, I love music. The classics, of course.
Mr. Burt: What's this about numbers?
Scully: Will you just...
Mr. Burt: I'm very good with numbers.
Reyes: The killer is driven by an impulse we believe is numerological.
Mr. Burt: Of course. He's a serial killer.
Scully: No, that's... that's not what she means. She thinks that his acts are determined by a calculation of numbers.
Mr. Burt: So the killer is not in control of his actions - the numbers are.
Mr. Burt: Well, are the numbers helping you catch him, or are they helping him not get caught?
Reyes: That's a good question.
Scully: Sir, does it look like we're here to play checkers?
Scully: There's a pattern in the bruising. All four of the victims have it. Three small circles. It might be from a ring that the killer wears.
Reyes: So you're saying these cases are connected? That numerology may actually be driving the killer, and that I'm definitely not crazy?
Scully: Or that maybe you're both crazy.
Reyes: (answering phone) Hello?
Scully: All right, I need to know.
Scully: What my numerology is, and what my number... whatever you call it. What am I?
Reyes: You're a nine.
Scully: Which means what?
Reyes: Nine is completion. You've evolved through the experiences of all the other numbers to a spiritual realisation that this life is only part of a larger whole. Dana, are you there?
Scully: There's something else that's bugging me.
Reyes: What's that?
Scully: Who was that man?
Reyes: God knows.
Mad Wayne: Go to Hell!
Mr Burt: Are the reservations in your name?
Scully: Sir, what are you doing here?
Burt: Waiting for a friend.
Scully: At midnight, in a parking garage?
Burt: We have this regular game we play.
Reyes: What kind of game?
Scully: Keep your hands up!
Scully: I don't know!
Special Agent Fordyce refers to the profile of their suspect as having a rage stemming from a hatred of his mother and was a bed wetter.
This also refers back to Scully in Piper Maru, back in season 4, saying that the FBI Could track a suspect right down to a killer's attitude towards his mother and that he was a bed wetter.
The songs played in this episode are from Karl Zero and they are: 'Ça va ça va', 'Torero', 'I love you for sentimental reasons', 'Ponciana', 'La pense', 'Inouis', 'Io Mamate e tu' and 'El Bodeguero'
Props department crew member Tighe Barry plays a homeless man in one scene of this episode.
Former Production Assistant-turned-Actor Angelo Vacco makes his fourth and final X-Files appearance in this episode. He previously appeared in the episodes F. Emasculata (Season 2), Talitha Cumi (Season 3), and Milagro (Season 6).
Chris Carter's "Executive Producer" credit at the end is in Italian.
The usual "The Truth Is Out There" tagline at the end of the opening credits is replaced with "Dio ti ama" - Italian for "God Loves You". Presumably this is a reference to what might be the true nature of "Mr. Burt".
Cultural Reference: Ace of Spades
At the end of the teaser, Mr. Burt is turning over cards, naming the cards just before they're shown. A woman enters the room screaming about a murder, and the final card Mr. Burt turns up is the ace of spades. In divination with standard playing cards (as opposed to Tarot) the ace of spades is the death card. This card was placed on the foreheads of killed enemy combatants during the Vietnam War.
Reyes: "God doesn't play dice with the universe".
Reyes quotes Albert Einstein in a very loose translation. In Einstein's native German, the quote was "Raffiniert ist der Herr Gott, aber bösehaft ist er nicht." A more literal translation of this is "God is clever, but he is not perverse."