The only connection I know of between snot and fiddles is a running joke among my musician friends about wiping boogers on fiddle bowhair. A fiddler will come back from a smoke or bathroom break and be told that so-and-so wiped boogers on her bowhair while she was gone. (Yes, it's juvenile, but you know how silly things can get between tunes at sessions.)

That's probably the source of the fiddle-related Google ads. It's pretty scary considering that I've never mentioned it before which means that Google read my mind.