Also Sprach Zarathustra is a song sung by Emperor Doofenshmirtz in "Phineas and Ferb's Quantum Boogaloo". Its tune is based on the emponymous song. The song was sung again in the episode "Phineas' Birthday Clip-O-Rama!", first by Irving and then again by Candace. It was sung again in the episode "Where's Perry?" by Phineas Flynn, as a way of making a callback to Irving's performance of the song in "Phineas' Birthday Clip-O-Rama".