Okay, I haven't told this story for a long time, and it's Christmas, so here we go:
When I was dating my first wife, I went to her parents for Thanksgiving dinner. Among the dishes on the table was blackberry jello with grapes in it. Seemed like a 50s kind of dish, but whatever. I took some of everything, and planned to clean my plate. My future MIL was telling a story when I put the first bite of the jello in my mouth, and my brain screamed that something was horribly wrong. I thought there must have been something rancid in the jello or the grapes - the grapes didn't even have the right texture. I was about to spit it out - it was revolting - when I realized it was a taste I'd had before, not something rancid. All this was really just a moment, but it seemed like forever before it clicked: it wasn't grapes, it was green olives. She made blackberry jello was green olives in it.
I thought for a moment that it was a prank, though that family wasn't the pranking type, because no one else had taken any except the mom, but she had a mound of it and was eating it. I finally said, "It was surprising to bite into a grape and find out that it's an olive," and everyone tittered. Future MIL said that no one else likes it, but she does, so she makes it for herself.