This is a personal favorite for both Gillian Anderson and David Duchovny who spent most of the shoot in hysterics.
Writer Vince Gilligan said that originally he wanted wings to be the "deformity" that the babies were born with, because he was afraid that tails wouldn't be very cute. Tails proved much easier to create digitally, though, so the wings were changed to tails in the script.
Despite his constant explanation that "the H is silent," various characters mispronounce Eddie Van Blundht's last name. The shot of the H falling off of the family name on the wall of his father's house is a nod to this frustration. It is also a reference to the fact that early in his career, series star David Duchovny's name was often mispronounced, largely because of the presence of a silent H in its spelling. Duchovny's father, the writer Amram Ducovny, had in fact taken the H out of his spelling of the name years earlier to avoid the constant mispronunciations, though David, his sister, and his mother all retained the original spelling. So the H literally dropping off the side of the Van Blundht father's house is also a reference to the H that Duchovny's father figuratively "dropped" from his name.
A return to the show of Darin Morgan, one of its most celebrated writers. This time, however, Morgan wasn't writing the episode but playing the lead guest actor spot.