to mcgrath of harlow.mouth music is more like melodic improvisation.
   chordal improvisation, bears no resemblance to mouth music or what we call here in ireland diddling or lilting.
diddling or lilting, first came about because the English tried to ban the playing of musical instruments in Ireland, so the Irish kept their traditonal culture alive .by singing the tunes, it is a very simple form of melodic improvisation, because they wouldnt have sung the song the same way every time.
but to call improvisation, mouth music is an over simplification, as I say chordal improvisation is not mouth music.