A ramble then a question :-)
I remember being shown a list of foreign body complaints a number of years ago from a major retailer. I remember that metal was the top one, with plastics, hairnets etc. and then bone, stone etc. further down the list. My thought is that there are two types of contaminants, ones dangerous to health and ones that could cause a consumer complaint. Consumers seem less likely to be upset if the contaminant is organic especially one that was a part of the product, like bone for example.
Obviously the ones most likely to be injurious are metals and glass. Stone can break teeth, bones the same and potential choking, and then plastics if they are big enough could be a choking hazard. Other than that its really brand protection.
So when we test our inspection systems we use Ferrous, Non Ferrous and Stainless Steel for metal detectors and typically stainless steel and soda lime glass for X-ray based systems. There are lots more contaminant types out there but not commonly used.
My question is really - what foreign bodies are most common and which ones most likely to cause a customer to complain?