10 Scariest X-Files Episodes Of All Time

6. Folie à Deux - Season 5, Episode 19

Anyone who has worked in a call centre can relate to Gary Lambert, a man who, trapped in the world of his tiny office cubicle, starts to lose his grip on reality and imagines that his seemingly decent boss is actually a giant monster, bug-type thing. So he does the only rational thing he can and takes the entire building (and Mulder) hostage in order to prove it.

Lambert dies but passes on his delusions to Mulder, who also begins to see the monster. It is a very scary thought, being the only person who sees something wrong but no-one will believe you. But the episode itself was very nearly ruined and, apparently, wouldn't have been scary at all were it not for the help of computer technology.

The suit of the monster was laughable, according to most who worked on the shoot and, to get around the problem extensive post-production work needed to be carried out. The monster needed to be removed from all of the scenes, animated, re-entered with a speed blur and aided with buzzing sound before it could become truly scary.

This is one of the rare occasions when you could actually believe that Mulder was in serious trouble and seeing him strapped down to a hospital bed while ostensibly going insane made for some nail-biting television.