It seems you're almost never going to get a pure product since the world is made up of so many different things. While that may seem obvious, check out some of the disgusting things you may not have considered actually end up in your food:
Animal Excrement

Asparagus “Thrips” And Aphids

Berries And Insect Larvae

Aphids In Frozen Broccoli

Cigarette Butts

Cockroaches And Insect Parts In Chocolate

Fruit Flies

Insect Excrement

Maggots In Marashino Cherries

Mold And Rot

Rodent Hairsy Peanut Butter

Sand And Grit

Sticks And Stones

Very Moldy Tomato Paste

Thousands Of Insect Parts In Oregano

Parasites
