I was staying with my grandma and cousins during the summer holidays a few years ago and we went over to my great aunt's house for a family meal. My grandma usually brought along leftovers, but this time, the only Tupperware she brought was full of food for our dog : cartilage and old chicken intestines mixed in leftover sauce. My great aunt saw this Tupperware in the fridge, and mixed it into her sauce, not knowing its true contents.
We proceeded to have the most awkward family meal ever, wherein everyone silently ate this disaster of a dish, not daring to insult my aunt by calling out the weird texture and really funky taste. Only at the end of the meal did we realize what had happened.
I guess the lesson here is label your Tupperwares guys !