Humbug

Gillian Anderson's character Scully was supposed to eat a cricket in front of Mulder. After Scully picked it up, the scene was to be stopped so a candy bug could replace the real one. However, before "cut" could be called, Anderson immediately placed the real bug in her mouth and ate it, and it stayed in the final cut. David Duchovny's off-screen gross out can be seen in one of the many "Making of the X-Files" featurettes.

After the first victim is killed, Mulder tells Scully the victim suffered from ichthyosis. He then proceeds to explain to her what it is, however, as a doctor and pathologist, she would know about this condition. She also fails to stop him and lets him finish his explanation as if she didn't know what it was.