Remember that gold and silver would not work for most stringed instruments - they are malleable at room temperature and would stretch, getting thinner and thinner the more you stretch them. I think brass would be okay, but not iron. The big advance came when steel was developed.

Getting back to HUMAN GUT -- oh boy! What to do with your enemy's bones and guts .. no good to eat, so use the intestines for bowstrings and harp strings. Make flutes from his bones, serves him right! == Johnny