The episode: “The Saga of the Viking Women and their Voyage to the Waters of the Great Sea Serpent,” ep. 317. (Note: This title was so long that even the MST3k writers just called it “The Viking Women and the Sea Serpent.” Who knows what Roger Corman was thinking.)
The riff: Pointed out by Crow right as the film opens with a fancy-looking leather-bound book, which opens to show the title card.
The explanation: In the mid 1980s to 1990s, the famed soap opera “All My Children” used an opening sequence that looked almost identical to this one. It’s an obvious reference to someone who was watching soaps during that period. To others, they might recognize the “All My Children” reference, but the sight gag portion of it is clearly meant for those who know that “All My Children” starts with a big, leather-bound book being flipped through.
Novelty factor: I recognized the meaning of the gag when I heard it. I think I may have understood because of vauge memories of the soap operas that my mother used to watch–“Days of our Lives” and “General Hospital” standing alongside “All My Children” as her favorites. Interestingly, I am finding that memories of my mother’s tastes keep recurring in this project, as they did in the “Kalgan, blow me away” riff.