Character mistake: Vassily Peskov speaks Russian with a strong accent. This is because the actor who plays Peskov (Jan Rubes) was from former Czechoslovakia.
Musings of a Cigarette-Smoking Man - S4-E7
Character mistake: Ramón Mercader did not assassinate Leon Trotsky with an ice pick, as Frohike claims, but with an ice axe. (00:03:00)
Answer: As he stated many times throughout the series, Mulder needed Scully to be sober and skeptical. Whenever Scully's skepticism wavered and she started questioning her own rationality, Mulder would try to restore her sense of skepticism, because he needed her to be clear-thinking.
Charles Austin Miller