Dianna Agron (Quinn Fabray) was the last person of the original cast to get a part. On her first day, she had to do a scene with Cory Monteith (Finn Hudson) in which they made-out together. Director Ryan Murphy told her to look sexy, but she was so nervous that she couldn't focus.
The scene where Rachel reprimands Finn for quitting glee club originally ended with her slapping him. In her audition, Lea Michele reached across the table without any hesitation and slapped one of the casting directors who was reading Finn for her. When the other casting directors erupted with laughter, Michele sternly told them, "This isn't comedy, that was my sad face! Now, I'm going to do it again, and you're all going to cry."
Kurt sings the song "Cellophane" from Chicago. Chris Colfer sang the same song for his audition for the show.
Rachel (Lea Michele) sings "On My Own" from "the seminal Broadway classic 'Les Misérables'" for her Glee Club audition. While still a small child, Michele made her Broadway debut as an alternate for the roles of young Cosette and young Éponine in "Les Misérables", and later was offered the role of adult Éponine (the character who sings "On My Own" in the show). Michele turned down the chance to play adult Éponine, so that she could stay with the "Spring Awakening" production (which she had been with since its first workshop days) when it moved to Broadway.
Originally, the role of Principal Figgins was written for a white male, but Iqbal Theba won the part.