Bruce Harwood once trained as an ice skater, so he was quite at ease in the scene where the Lone Gunmen go skating. Dean Haglund on the other hand had never skated, so he under went a 5-day crash course in how to stay upright on the ice.
"Foo fighters" is the name given to UFOs observed by US Navy and US Air Corps pilots/air crew during WWII.
Craig Warkentin plays the role of the young Cigarette Smoking Man. William B. Davis (who plays the role of the present-day Cigarette Smoking Man) dubbed the voice to make the character sound more like his later self.