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.
After Digit brings back another gleamer bug to power the ship, the Cybersquad is surprised to learn that they have 30 gleamers of power, not 24. Jackie points out that the bug that Digit brought is actually two bugs stuck together. They use variable substitution to explain to Digit how they have 30 gleamers of power and to determine the number of additional gleamers they need to start the ship.
Elaine and her old boss find that selling just the tops of muffins is more profitable than selling the whole muffin (which consists of the top + the stump). So are the top and the stump complements or substitutes? Neither--the stumps are an economic bad, which reduce utility. Evidence for this is found in the fact that homeless people won't eat the stumps that the muffin-top restaurant throws away, unless they come with the tops as compensation.
Jerry is dating a girl but really wants to date her roommate. George suggests that the only way to make the switch is to propose a menage a trois to his current girlfriend, which will turn her off and her roommate on. Jerry follows through on George's plan, and finds that both girls are "into it." But Jerry can't follow through—and George can't believe it. To Jerry, the roommates are substitutes; to George, they are complements.