You know those little packets of dessicant you sometimes find in your food? This prompts the same thought every time I find one in my pepperoni package. Even through they are placed in the food, they come with a notice on it: do not eat.
It's obviously a tough pice of unedible plastic. I would not want to eat it even if I was very hungry. But maybe this is actually a conspiracy to enact some revenge on illiterate dumb people. They are dumb enough to eat a big piece of plastic and illiterate enough to not be able to read the warning.
That makes no sense at all.
Every time you read an obvious warning like that you have to wonder who's the kind of people who would do that. Do not eat this piece of unedible plastic. Do not stick your hands, or head, or any body part outside of the train window. And perhaps my favorite, No smoking at gas stations.