I was hoping it was a byproduct of recycling waste. Mystery creates buzz. The danger of a mystery food is part of why hot dogs and food cart food as a whole are popular.
What? Who eats hotdogs and food carts because of the mystery? I eat hot dogs cause they are fast, cheap, and delicious tubes of fatty salty meat. I eat food cart food cause it's just fucking delicious. I don't know the exact spec, but the Halal meat-on-a-spit is almost always lamb and beef doner kebab. The sauce is mostly yogurt, mayo, dill and oregano. I make my own sometimes.
Here is a fun filled article about the history of the hot dog. The time of "The Jungle" and mystery meat reminded me of the hidden origins of the plant in the original story: https://www.thehotdog.org/history-of-the-hot-dog/
https://en.m.wikipedia.org/wiki/Doner_kebab