Scully takes some time off from Mulder and discovers a man with a jealous tattoo.
In Philadelphia, Ed Jerse loses a divorce settlement to his ex-wife, who has sole custody of his children. After getting drunk at a local bar, Ed wanders into a tattoo parlor and impulsively receives a tattoo depicting Bettie Page. He is then shown to return back to his home, to collapse after viewing the new tattoo. At work the next day, Ed hears a woman calling him a "loser"; he has a violent confrontation with a female co-worker—who denies saying anything—and is subsequently subdued.
In Washington, Agents Fox Mulder and Dana Scully conduct a discreet meeting with a Russian informant, Vsevlod Pudovkin, who claims to have seen a UFO at a secret research center. Upon returning to FBI headquarters, Mulder heads out on vacation, leaving Scully to follow up on the Pudovkin case for him. Scully is uninterested in the case and expresses serious doubts about Pudovkin's credibility, leading to an argument with an inconsiderate Mulder. Scully becomes upset over the direction her life and career are going.
At his home Ed is called by his boss and is fired. He hears the same voice as before, and yells at the woman living below him, thinking it was her. Upon hearing the voice after a pair of Jehovah's Witnesses stop by, Ed goes downstairs and murders his neighbor, throwing her body in the furnace. The voice talks to him again and he realizes it's coming from his new tattoo. Scully heads to Philadelphia where she watched Pudovkin enter a tattoo parlor. Scully heads inside where she sees Ed arguing with the owner, wanting the tattoo to be removed.
Ed strikes up a conversation with Scully and invites her out to dinner, to which she replies she has other business to take care of. That night Scully talks to Mulder, who is in Graceland, telling him that Pudovkin is a con man and part of the Russian mafia. Scully calls Jerse and tells him that she changed her mind. The two head to a nearby lounge but she is concerned about Ed's arm, where he has burned the tattoo with a cigarette butt. Ed convinces Scully to get a tattoo, and she has one of an Ouroboros applied to her back.
That night Scully stays at Ed's apartment. The tattoo is angry at him, saying she'll be dead if he kisses her, which he does anyway. The next morning two detectives arrive at the apartment after Ed has gone out, who tell Scully that Ed's neighbor is missing and blood was found in her apartment with an unusual chemical substance in it.
Scully researches the material on Ed's laptop and tries to call Mulder at the FBI headquarters but hangs up before Mulder has a chance to answer. When Ed arrives Scully tells him that they found blood in his neighbor's apartment and that it was likely his. She thinks that the chemical came from the tattoo ink and wants them both to head to the hospital to be tested. Ed tells Scully about the voice he's been hearing from his tattoo. As Scully heads to the other room to get ready, her FBI badge falls out of her coat pocket. Scully discreetly picks it back up without Ed noticing.
Then, the tattoo begins to talk again, convincing Ed to redial Scully's last call to see who she was speaking to. An FBI operator answers and, upon learning that Scully is a FBI agent, the tattoo forces Ed to attack Scully. Scully tries to escape but is overpowered by Ed, who binds her in a bedsheet and carries her down to the basement to throw her in the furnace. At the last moment Ed is able to overpower the impulses of the tattoo and instead thrusts his own arm into the furnace.Scully returns to Washington and is congratulated by Mulder for being the first person to make a second X-File appearance. Ed was brought to a burn center in Philadelphia where the chemicals (ergot) were found in his blood, also in Scully's blood but not enough to cause hallucinations. Mulder wonders if this all happened because of their earlier argument, to which Scully replies that not everything is about him.
- Ed Jerse's address was 1951 Young Street, Philadelphia, PA 19152; his phone number was (215) 555-0157, fax (215) 555-0158.
- Scully got a tattoo of a circular snake with its tail in its mouth in her back in this episode. This is an Ouroboros—it has been used to represent many things over the ages, but it most generally symbolizes ideas of cyclicality, unity, or infinity.  The Ouroboros was also the symbol of the Millennium Group in the television series Millennium, produced from 1996 to 1999 by Chris Carter.
- The song playing in the background in the bar opening is Tattooed Love Boys by The Pretenders from their 1980's debut.
- This episode establishes that Mulder doesn't like to take vacations.
- The magazines in the birdcage that the downstairs neighbour has is an Entertainment Weekly cover with David Duchovny on it.
- Jodie Foster is the voice of the tattoo as well as the frightened co-worker in the cubicle with Ed's boss.
- The selection of Jodie Foster as the voice of the tattoo which talks to Ed Jerse is perhaps a reference to John Hinckley, Jr., who claimed he was motivated by Jodie Foster to assassinate President Ronald Reagan.
- Originally slated to direct this episode was an Academy Award winner Quentin Tarantino, but the Director's Guild of America disallowed it.
- Gillian Anderson volunteered to have the ouroboros tattooed onto her back for real during filming. This could not be done due to the fact that it would take too long and would have been impractical.
- The song that plays while Scully and Ed Jerse sit together in the Hard Eight bar is "The Have Nots" from X's 1982 album, "Under The Big Black Sun." The song's lyrics are uniquely suited to the bar scene.
- Ed Jerse's favourite bar is named 'Hard Eight' for the production company of writers Morgan and Wong.
- Guest voice Jodie Foster played Agent Clarice Starling in Silence of the Lambs. This character, and Foster's portrayal of her, were Chris Carter's original inspiration for the character of Dana Scully.
- Kaye Shilling, the downstairs neighbour shares her name with an Entertainment Weekly editor Mary Kaye Shilling. The writers of this episode were unhappy with some recent reviews in EW, so it is no shock to see character Kaye Shilling lining her birdcage with the magazine. (The cover of said magazine featuring X-Files producer Bob Goodwin and declaring him 'The wisest man in Hollywood.')
In the DVD audio Betty is constantly alternating between left and right channel in stereo. This gives the illusion that Betty is also in the audience's head as well.
When Ed Jerse bangs on the floor in his apartment, the girl downstairs cranks up the stereo, playing the Partridge Family song "Doesn't Somebody Want to be Wanted".
Scully logs on to fbi.lab.rl.fns.gov/forensics to check the poison information. There is nothing at that site currently.
The camera angles and long tracking shot backwards down the stairs are a conscious homage to a similar shot in Alfred Hitchcock's Frenzy.
Scully's analysis of the blood information shows the presence of ergot. Her explanation of the matter is succinct but correct. Ergot is a fungus that contains hallucinogenic alkaloids (LSD was originally discovered in ergot derivatives); it grows on grasses and grains, including wheat, barley and rye, from which it finds its way into flour and thence into baked goods. Scully mentions that the red tattoo ink was made from rye. It has been suggested that the hallucinations which resulted in the accusations leading to the 1692 Salem Witch Trials were the result of ergot poisoning. Records of outbreaks go back 1200 years, and have occurred as recently as 2001.
The Republic of Karelia (Республика Карелия) is a real place, located at the border between the Russian Federation and Finland. A part of Russia, it has a level of autonomy roughly equal to a US state, with its own internally elected governor and assembly. At various times ruled by Finland, Sweden or Russia, Karelia has a rich poetic and musical heritage which figures significantly in the traditional culture of Finland. Finnish composer Jean Sibelius was inspired greatly by folk music of the region.
Scully tells Ed Jerse that her last date was to see Glengarry Glen Ross, and that "...the characters had more fun than I did." The 1992 film, based on a play by David Mamet (who also wrote the screenplay), takes place in a real estate office with an extremely high-pressure sales incentive program. Praised for its drama by some, the film and the play are considered tedious and lacking action by others. Presumably, Scully is one of the latter. Assuming both that the show's chronology roughly matches the original broadcast dates and that Scully saw the movie when it was first run, this means she has been dateless for nearly five years.
When Mulder calls Scully's hotel to see if she is in her room. The hotel receptionist puts Mulder through to Scully's room where it is only allowed to ring twice before it is disconnected and the receptionist tells Mulder there was no one there. Surely they would wait a while longer for an answer.
After Scully walks away from Eddie in the his apartment and drops her FBI identification, there is a close-up of Eddie's tattoo with no cigarette burn. The next shot when Eddie is putting the phone receiver to his ear, the cigarette burn is clearly visible.
Cast and Characters