The US Marshal Service does not have its own ambulance trucks.
In the beginning of the episode, the chief engineer sends Dmitri to check what's clogging the sewage system. After Dmitri is pulled into the water by the flukeman, he gives the order to flush the tank. If that's an option, how come they didn't flush the tank before Dmitri started his work? It would make it easier to search for cloggs.
Factual Errors: Scully states that a hermaphrodite is an animal with no sex organs. However, a hermaphrodite has both male and female sex organs.
Plot Hole: Given how dangerous the flukeman is meant to be, why is only one US marshal put in charge of it in the ambulance? And why does the marshal radio for back up only to end up going into the back of the ambulance by himself?
Factual Errors: Scully reads to Mulder from a book all about flukes (Trematodes). However, the stuff she is quoting is wrong! She states that flukes or flatworms have a scolex with hooks and suckers. These are actually the distinguishing characteristic of cestodes (tapeworms). Trematodes have no scolex and definitely no hooks.
Scully: And Mulder, when you see Skinner to hand in your field report, I know that is your decision but I hope you know that I'd consider it more than a professional loss if you decided to leave.
Scully: Is this seat taken?
Mulder: No, but I should warn you I'm experiencing violent impulses.
Scully: Well, I'm armed. So I'll take my chances. I hear you really endeared yourself to Assistant Director Skinner today.
Mulder: Sometimes it just gets hard to smile through it when they ask you to bend down and grab your ankles, you know?
Scully: It's not exactly as if you've ever tried to fit into the program.
Scully: Is this seat taken?
Mulder: No, but I should warn you I may reek a bit of the sewer.
Scully: I'll take my chances.
X: I think you should know...you have a friend at the FBI.
Scully: That creature came off of a decommissioned Russian freighter that was used in the disposal of salvage material from the meltdown. It was born in a... in a primordial soup of radioactive sewage.
Mulder: You know, they say three species disappear off the planet every day. You wonder how many new ones are being created.
X: Mister Mulder, I will make this brief. Success in your current assignment is imperative.
Mulder: Who am I speaking to?
X: Are you hearing me, Mister Mulder?
Mulder: Yes. Why is it imperative?
X: Reinstatement of the X-Files must be undeniable.
Mulder: You know, you had a pair of agents that could have handled a case like this. Agent Scully and I might have been able to save that man's life, but you shut us down.
Skinner: I know. This should have been an X-File. We all take our orders from someone, Agent Mulder.
Skinner: The justice department has asked that the suspect be transferred to an institution for a full psychiatric evaluation.
Mulder: This is not a man. It's a monster. You can't put it in an institution.
Skinner: Then what do you do with it, Agent Mulder, put it in a zoo? It killed two people.
Scully: Platyhelminthis are often hermaphroditic. Mulder, this is amazing. It's vestigial features appear to be parasitic, but it has primate physiology. Where the hell did it come from?
Mulder: I don't know, but it looks like I'm going to have to tell Skinner that his suspect is a giant, blood-sucking worm after all.
Scully: Flatworms are what are known as obligate endoparasites. They live inside the host, entering the body through the ingestion of larvae or eggs. They are not creatures that go around attacking people.
Mulder: Well, that's good. I didn't want to have to tell Skinner that his murder suspect was a giant, blood-sucking worm.
Scully: It's called Turbellaria, or it's commonly known as a fluke or flatworm.
Mulder: This was living inside the body?
Scully: Apparently, it had attached itself to the bile duct and was feeding off the liver.
Scully: Believe it or not, something like forty million people are infected worldwide.
Mulder: This isn't where you tell me some terrible story about sushi, is it?
Scully: Well, maybe you'd rather hear what you can catch from a nice, rare steak.
Mulder: So, what, the murder weapon was a top sirloin?
Mulder: Any idea what attacked you?
Workman #1: Yeah, I've been thinking it might have been a python.
Mulder: A python?
Workman #1: Yeah, or a boa constrictor. Somebody probably flushed a pet snake down the toilet. I found an alligator in the sewer a couple of years ago.
Mulder: They don't want us working together, Scully...and right now, that's the only reason I can think of to stay.
Mulder: Any I.D.?
Norman: No. Not much to go on either. Front side of the body is pretty much eaten away. Would you like us to turn him over for you?
Mulder: No, I'll take your word on that.
Norman: Hey, Agent Mulder. What would you like us to do with the body?
Mulder: Wrap it up and send it to the F.B.I., care of Assistant Director Skinner.
Gabrielle Rose returns as Dr. Zenzola: she previously appeared in the episode "Deep Throat."
During Scully's autopsy of the victim, she says the case number is DP112148 (CC's wife's birthday) preceded by her initials. She says the victim is John Doe 101356, Chris Carter's birthday.
The Flukeman suit took up to 6 hours to put on. At one point, Darin Morgan, who played the part of the Flukeman, had to wear the suit for 20 hours consecutively. Because the suit was so difficult to remove, that meant that Morgan had to relieve himself in the get-up.
Darin Morgan, who plays the Flukeman, is the brother of co-executive producer Glen Morgan and later became a writer for the show.
Originally X was intended to be a woman and actress Natalia Nogulich was first cast before the character was changed.
This episode marks the first appearance of X, Deep Throat's successor as Mulder's confidential source who phones him to say that he has 'a friend in the FBI'. Although the actor on the phone isn't Steven Williams, the voice was dubbed over with Williams' after he was cast in the part for "Sleepless."
Mulder: I know these. These are from Chernobyl.
Mulder is referring to the explosion of the Chernobyl nuclear power plant in 1986. The cloud of radioactive material that was released that day, still makes victims every day as the cloud increases the chances of cancer and physical abnormalities. The site of the explosion is still policed and the clean-up continues till this day.