U-shaped Curves

I was reading recently about U-shaped toxicity curves (compounds that do not show a linear dose dependence for toxicity). Mechanistically, they don't seem to make sense, at least not at first... but then I have realized that I have a U-shaped preference for chocolate. I am not a chocolate fanatic like some people... but I do like sweet milk chocolate. I recently enjoyed a dessert wine/chocolate tasting, and I discovered that while I don't really like the standard "dark chocolate", I do like the super dark stuff.