The kids were guessing the ingredients of the stroganoff sauce.
Thinking about salt, I gave them a hint: "It's very small, you can't see it, but it's present in almost all food."
Said the 7yo: "Microplastics!"
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So i would guess this is not the answer you are looking for here, but would it still be a correct answer ?
@zleap @victorgijsbers I think ingredients are things you mean you put in by design. Contaminant would be the word for microplastics in a sauce.