Yep Mitch..you're very correct. There is a legal filth content in food. When I was teaching it used to gross the kids out when I would tell them that when food inspectors pulled products off the line to inspect them that there were just so many fly parts or rat hairs, etc that were legal before they would close a plant.
But I just returned from a 10 day camp-out...sure that I have eaten my share of "filth" and I am positive that I snorted my share of gnats and mosquitoes! Dang it was fun!