Rain can be heard when Fox and Scully are standing outside the car after visiting the cemetery but there is no rain falling on the car or the actors. There was most likely a tarp over the actors but the audio was not corrected.
(In the sixth minute) When Mulder begins to ask Scully how a "six foot four two hundred and fifty pound man could be buried alive in less than five minutes by a sixteen year old whose classmates lovingly refer to as dork-weed?" Mulder's mouth is saying "dickweed".
The teacher writes the molecular formulas for sodium chloride and hydrogen chloride wrong. The correct formulas are NaCl and HCl; she writes NaCl2 and HCl2.
The first time he talks to the boy, Mulder translates "Ich bin ein Ausländer" as "I'm an outsider" but it actually means "I'm a foreigner" as in "I'm from another country." The correct German for "outsider" is "Außenseiter".
Mulder says that John F. Kennedy's famous words "Ich bin ein Berliner" mean "I am a cocktail sausage". In fact there is a common misconception that JFK said "I am a jelly doughnut," when he meant to say "I am from Berlin."