At the opening of the episode, Darlene Morris burns her left hand trying to open the RV door, then wears an oven Glove only on her left hand. She opens the door again but this time with her both hands without any harm to the naked right hand.
In Samantha's personal X-File, her middle name is only listed as 'T', while in several other episodes it is Anne.
Before Kevin hands the pad to Mulder you can see that some of the shapes are filled in. But after Kevin hands Mulder the paper the shapes are just outlines, and it doesn't appear that pages were flipped.
When Mulder is running after the boy near the end, and the motorcycles are coming, we see him throw the torch quite far away, yet when the motorcycles are gone we see it is right next to him.
At the end of the episode watch the small cross that Scully wears as she and Mulder walk down the hall. When the shot changes to a close-up, it has jumped into her shirt.
When Ruby is discovered late in the episode, Scully is seen administering CPR on her with a gentle pulsing motion. In fact, CPR requires firm thrusts which have been known to break ribs. The mild movements made by Scully are unlikely to have any resuscitative effect.
When Mulder and Scully go to Okoboji, IA the title on the screen reads Okobogee, IA. This is misspelled every instance it occurs in the episode, including the captioning and the sign their car passes on the way to the lake.
At 26m 55s the photographer is holding a flashgun, takes a picture, but the flash does not fire.
The real Lake Okoboji in northwest Iowa is nothing like the Lake "Okobogee" depicted. Okoboji is actually two lakes (East Lake Okoboji and West Lake Okoboji) nestled among a grouping of about a dozen other nearby lakes. In the summer, the Okoboji area (aka "Iowa Great Lakes") is a densely populated tourist/resort region, not the remote, forested area shown here. There's no trout in the lakes either. Maybe they meant walleye.
At around the 13 minute mark, as they leave the sheriff's building, a boom mic is visible moving between the cars as they walk along.
At the lake Mulder finds a piece of glass made from sand on the beach. He says that lightning couldn't do that. In fact, lightning commonly turns silica (sand) into glass called fulgurite.
(at around 39 mins) Mulder asks Scully about any mention of attendant reduction of lymphocytes or release of glucocorticoids, explaining them to be the "symptoms" of prolonged weightlessness.
Actually, these findings are the "signs", and not symptoms. The two terms have different meaning in medical parlance. In lay person's parlance, signs are what the doctor notes and symptoms are what the patient reports.
Mulder refers to the adult leader of a Girl Scout troop as a "den mother". Den mothers are in charge of Cub Scout troops. Adults in the Girl Scouts are simply referred to as "troop leaders" or "scout leaders".
In Samantha Mulder's file, the name of the town of Chilmark, Mass., is twice misspelled as Chilmarc, Mass.