BLAT!
The burlap sack is silent. So is the saxophone inside, even though there is a skilled blues artist attached to it. So why is the bluesman’s sax silent? Easy. Does tree make a sound when it falls in the woods if there’s someone around to hear it? Sure, if you’re not deaf.
But these aren’t the real questions. Why would a saxophonist and his tool of trade be in a burlap sack?