This story made my jaw drop
You have to listen to the story to hear the bit that alarmed me. But the gist of it is, in order to make bigger profits from the popularity of olive oil, manufacturers commonly dilute the olive oil with other oils, and one of the most common replacements is hazelnut oil! And of course it wouldn't be labeled as such since they're trying to pass it off as real olive oil.
I wonder how many people's mystery reactions are from something like this?