"The Substitute" includes a short "fantasy" moment. In it, Will sees the club members as kindergarten-aged children. Child actors were used to act out as the characters' younger selves. These included Jake Vaughn and Lauren Boles as young Finn and Rachel. The episode also includes the return of Gilsig. Gilsig had not been in several episodes of "Glee". Gilsig believed that Will's sickness let viewers see the couple in a positive relationship for the first time. She also thought that the addition of Holly "highlighted" a special bonding in their relationship. She said that while Terri is not "the most pleasant person", she is at least faithful to Will, while he has "a wandering eye" (has interest in another women) and treats Terri badly in "The Substitute". The main characters in this episode include glee club members Mike Chang (Harry Shum, Jr.) and Sam Evans (Chord Overstreet), Principal Figgins, school bully Dave Karofsky, cheerleader Becky Jackson (Lauren Potter), wrestler Lauren Zizes (Ashley Fink) and Kurt's friend Blaine Anderson.