The episode: “War of the Colossal Beast,” ep. 319
The riff: Exclaimed by Tom as Miguel, a terrified young Mexican boy, gazes up in a sort of trance from his hospital bed while police try to question him.
The explanation: “Bernadette” is a reference to Bernadette Soubirous, a young girl who had visions of the Virgin Mary in 1858 in France, and was later named a Catholic saint. These so-called “Marian apparitions,” which presented to several people, are the source of the title “Our Lady of Lourdes,” as Lourdes was the region of France where this all occurred. Tom is joking that Miguel’s expression conveys a moment of religious ecstasy where he is seeing Saint Bernadette.
Novelty factor: I had absolutely no idea. Moreoever, I am curious which of the MST3k writers penned this one. It seems safe to assume that at least one of them was raised Catholic. Note that the riff doesn’t say “Saint” Bernadette. They went out of their way to make this a joke that only another Catholic would probably understand right off the bat.