Enlever le bec et souffler dans la clarinette comme dans un cor.In this section of the Nonetto (#33) Villa-Lobos instructs the clarinettist to remove the mouthpiece and blow the instrument like a horn, singing the notes "comme dans un mirliton." The Mirliton is also known as a Eunuch flute or onion flute (flûte eunuque, flûte à l'oignon), or in Germany, Zwiebelflöte. It's basically a wooden flute with a thin membrane fixed at one end, through which one blows and vocalizes at the same time. A kazoo is a kind of mirliton, though I believe Villa-Lobos was imitating an instrument used by Brazilian Indian musicians.
Sinon chanter les notes, tres justes, dans le bec seul comme dans un mirliton.
You can hear the effect after 9:30 in this classic performance of the Nonetto by The Roger Wagner Chorale and The Concert Arts Ensemble.
The Nonetto was begun in Rio in 1923, and completed and premiered in Paris the following year. This is the high-water mark of Villa's modernism; it's leading-edge avante-garde composition.