At that time, it was not known that Duke had bipolar disorder, but Sheldon did notice that she had two distinct sides to her personality and thus developed the concept of identical cousins with contrasting personalities.
Nese momento non se sabía que Duke tiña desorde bipolar, mais Sheldon notou que a súa personalidade tiña distintas facetas, desenvolvendo o concepto das primas idénticas con personalidades opostas.