Season 4, Episode 7 - "Sophia's Wedding, Part 2"
Rose told The Girls that a St. Olaf motor coach company built a car called the Fenderhooven Rocket, but it never got off the ground due to bad promotion. She said it was the first car to run on free fuel. How was it powered?
By cow manure
Rose: I think a lot of people were turned off by the ad—a cow sitting on a gas tank reading the Farmer's Almanac.