Amy is mad at Sheldon, and he goes to the jewelry store with Penny to buy Amy something. Sheldon hints to the salesperson that diamonds are carbon just like charcoal, but it's only their molecular arrangement that makes them valuable. When the salesperson tells Sheldon that everything is on sale, Sheldon is suddenly more interested in a pocket watch he was previously considering.

Elaine is consulting a rabbi, who offers her Snackwell's Cookies. He says he fears that knowing they're fat free may cause people to overindulge. Making them fat-free lowers the price of eating them; consumers respond by eating more.

When George joins a book club to impress a girl and then finds the reading too costly, his demand for a substitute good (the video of the novel) rises to ridiculous proportions. In the end, he finds that the movie and the book are imperfect substitutes.

Kramer has invested in a fat-free yogurt shop, but Jerry and Elaine begin to gain weight after indulging in it.

When Sheldon alerts Penny that she'll earn over $3,000 for a single night of work, she imemdiately goes to buy shoes.