Little girls in masks played the aliens.
It won an Emmy Award for Outstanding Makeup for a Series.
In the decontamination shower scene, Mulder is played by a body double and Gillian Anderson is actually wearing a bikini.
In the opening scene, humans are shown coming into contact with the aliens on October 13, 1973. October 13 is also the birth date of show creator Chris Carter.
It took 15 takes - and 15 photographs - for director Rob Bowman to be happy with the opening shot of the picture of Mulder's father and a younger Cigarette Smoking Man going up in smoke.