From the recording True Story

Free

The mouthbow plays the harmonic series... the notes 1,3,5 and 8 of the major scale are most prominent and these are the notes that we usually hear at the beginning of a song to set the key or the fundamental tone the song is built on, in our minds.
So, you're sitting there in the dark playing with these notes and out pops a familiar tune... huh? oh Wow, that's cool... I wonder if I can find a way to play the rest of it. Mouthbow is so weak, it might be hard to recognize the tune unless I put some words to it...
The story I learned in grade school, music appreciation, was that Ravel was lying in bed in his hotel room in Paris. It was late at night, but close by a new skyscraper was being built and they were working on the steel framework. Ravel could hear the sounds of steel girders clanging against each other and the riveting never ceased. 
He heard harmony and dissonance in the clanging steel and a rhythm in the riveting.... Finally he got up and wrote it down.