In the beginning of the episode, when Mulder tells Scully "Prison, Scully. Your cellmate's nickname is going go be 'Large Marge', she's gonna read a lot of Gertrude Stein!" The camera cuts to Gillian Anderson covering her face with her hand, to appear frustrated with her partners words, but you can (if you look carefully) see her smiling behind her hand. OK, I'm not sure if this was intended to be a smirk on the part of Gillian's character in reaction to what David says, or if she's covering a giggle to prevent a cut of the shot. I'm inclined to think it was a cover because I'm sure most Philes know what a giggler Gillian is and when she gets going she can't stop. She does a good job of stifling it, though, as they continue the scene.