I repaired instruments for more than forty years and I've seen some interesting things. Some are readily explainable, others are more byzantine. One of the more interesting affectations that some people cling to is installing Rattlesnake Rattles in - usually fiddles, but occasionally guitars, banjos, dulcimers etc. For a long time I wondered about this as most people brought their instruments to me to get rid of "rattler" type noises.
We often see old-time fiddlers who Never (ever) wipe the rosin off of the tops of their instruments. This results in a white buildup under the strings which (in my opinion) ruins the finish and muffles the volume and tone quality. But it is not hard to look back to before W.W. II, when in rural areas refined rosin might have been a fairly hard to find luxury. Being able to run the bow under the strings to recharge it with the rosin on the face could have been a good economic choice - much like re-rolling used cigarette butts. Those of us who lived in the South Georgia/North Florida slash pine belt did not have as much trouble finding refined rosin as Turpentine stills dotted the area. Perhaps the rest of the nation wasn't as blessed as we were.
But back to the "Rattlers". I finally heard what I think is a logical reason for putting "rattlers" in an instrument. Prior to 1900, in most of the rural and God fearing areas of our nation it was common knowledge that a fiddle was "the devil's instrument". Without delving into the whys and wherefore of this, suffice it to say that the Good Lady of the house would not allow such a device into her home... Thus the humble fiddle was relegated to the barn - where existed, after all, the only indoor space large enough for a corn shuckin', dance, or other musical event. So it probably made sense to leave the fiddle out there. Barns do have mice though, and as a repairman I've seen what lengths a mouse will go to in order to make a fiddle into "Home Sweet Home". I even had to "restore" an example of such once, a family heirloom. Mercy.
At some point in history some observant fiddler noticed that if he put some rattlesnake "Rattlers" in his fiddle the mice stayed away. Mice are very aware of snake smell as it represents an early and effective form of pest control. These traditions are neither good nor bad, but I find it enjoyable to seek out their origins. "Rattlers" make fiddles mouse proof- even in a barn.