For that matter, the very thing he did was what mastered him into doing it.

No more than could he refrain from shaking the water from his back after a swim, or from kicking in his sleep when his feet were tickled, could he have avoided doing this imperative thing.
As her voice, in the song, made soft vibrations in his ears, it seemed to him that she grew dim and vague before him, and that somehow, under the soft searching prod of her song, he was otherwhere.

So much was he otherwhere that he did the surprising thing.

He sat down abruptly, almost cataleptically, drew his head away from the clutch of her hands and out of the entanglement of her hair, and, his nose thrust upward at an angle of forty-five degrees, he began to quiver and to breathe audibly in rhythm to the rhythm of her singing.

With a quick jerk, cataleptically, his nose pointed to the zenith, his mouth opened, and a flood of sound poured forth, running swiftly upward in crescendo and slowly falling as it died away.
This howl was the beginning, and it led to the calling him "Sing Song Silly." For Villa Kennan was quick to seize upon the howling her singing induced and to develop it.