Every Rick has an opening between its innards and the Outside World--it's the output jack. Factory woodworking, sanding, and buffing operations inevitably leave a certain amount of residue inside the guitar, even though the carcasses are blown out with compressed air guns many times in the course of construction.
This residue makes its way out and that's why you will find it in the case, usually in the area of the output jack.
“I say in speeches that a plausible mission of artists is to make people appreciate being alive at least a little bit. I am then asked if I know of any artists who pulled that off. I reply, 'The Beatles did.”
― Kurt Vonnegut