When Penny got drunk and spent the night at Leonard's, Mrs. Gunderson was able to hear them having sex, as she lives directly below them and they were making a lot of noise. The following morning when Penny heads to work, Leonard follows her down to the third floor and Penny tells him that them sleeping together was a mistake. When Penny leaves, Leonard shouts at her angrily and accuses her of using him for sex. As he makes this comment, Mrs. Gunderson exits her apartment. She and Leonard smile at each other and Leonard says good morning. Mrs. Gunderson says good morning as well, then jokingly says "Or, should I say, yee-haw?" a reference to what Leonard and Penny had been shouting during sex. She then winks at Leonard as he slowly walks away in embarrassment.