Grampa vs. Sexual Inadequacy

"Grampa vs. Sexual Inadequacy" is the tenth episode of The Simpsons ' sixth season.

Synopsis
When Homer and Marge's marriage comes under threat due to their fading sex lives, Grampa pieces together a tonic that is guaranteed to help the bad situation. The effectiveness of the tonic results in Homer and Grampa going into business together, selling “Simpson and Son’s Tonic” to the public. They travel from town to town selling the product, but when they visit the farmhouse where Homer grew up, the two have a disagreement. Grampa calls Homer an “accident” which makes Homer angry, but also causes him to change the way he acts as a father to his own children. He vows to show his children the attention they deserve, but they feel he is overcompensating, preferring the “old” Homer. He goes back to the farmhouse, coincidentally at the same time as Grampa, and after accidentally setting fire to the building the two both admit they are “screw-ups”. Thus creating a plot hole in the later episode "E-I-E-I-(Annoyed Grunt)", in which the Simpsons temporarily move to the Simpson farm.

In a subplot, Bart and friends attempt to figure out why all of the adults disappear after they buy "Simpson and Son's Tonic". They come up with numerous imaginative ideas, none of which have to do with the tonic.

Cultural references

 * Homer accidentally grabs a nutty photography book by Robert Mapplethorpe at the bookstore.
 * Lisa references Occam's Razor, a real 14th century theory.
 * Milhouse's line "We're through the looking-glass here, people" is from Oliver Stone's JFK.
 * Prof. Frink transforming into a suave man with a deep voice is a reference to Jerry Lewis transforming into Buddy Love in The Nutty Professor.
 * Abe Simpson is mostly seen dressed as a quintessential Southern Colonel, an image most associated with Colonel Sanders, the founder of Kentucky Fried Chicken.

Trivia

 * When Homer leaves to 'do some serious thinking' he drives away from the house in the red station wagon (Marge's car), but arrives at the farmhouse in his purple sedan.
 * When Homer and Marge are in the car, between scenes, the windscreen goes missing. It becomes noticeable when the mirror appears and disappears, and Abe's head manages to pop out when he and Homer argue over the getaway music.