why is foil so icky??

So here I am eating my nice chocolate bar, and it got kinda melted once and rehardened, and it seems a bit of the inner gold foil of the packaging stuck to some bit of the chocolate, and hence wound up in my maw ... and my teeth are absolutely revolted by said foil. ! Why? What is it about the foil that makes me get it out off of my tooth NOW? It's not a flavor thing or even a texture one, I just know my teeth really hate the foil. Is it a reaction to a mineral? I haven't tried eating rocks in a very long time...

Inquiring minds want to know.