A stand-out episode of “Supernatural,” for Kripke was Season 4’s episode "Lucifer Rising," of which he stated, “Later on in one of the drafts of the scripts, I crucified a nun, kind of bleeding down an upside-down cross, and Bob Singer came into my office, and he said, 'You know, Eric, I rarely say this, but you're going way too far.' And I said, 'Well, you know, nun violence is the last great frontier for us.”