Granted, this was some decades ago. But when I was in college, we had someone speak give a lecture, who was a higher up at a major pet food company. He said that research showed that some 25% of pet food was actually consumed by humans, so they needed to make sure the pet food was human grade. He claimed that one of their enforcement mechanisms for that was to have "surprise" buffets where workers and management at all levels of the company and product preparation, were required to eat some of the product.