From Zappa Wiki Jawaka
Pierrot Lunaire is a compostion by Arnold Schoenberg which uses a spoken singing style which Zappa would adapt for his own work.
"A speech-song. That means, instead of singing all the pitches of the song, you half speak it, you half sing it. It's a technique that was attributed to Schoenberg who used it in a piece called "Pierrot Lunaire". And the way it was written was: all the pitches for the soprano to sing, the ones that she was supposed to half speak, had X's on the stems. But I don't think he invented it because this is a type of vocal styling that has been used in Blues. It's also been used in other types of ethnic music. You can find it in Bulgarian music where, instead of exactly singing the note, you imply the pitch of the note, but you're really talking it. It's in between. (...) The first album had "sprechstimme" on it."