If you’ve gone on a few overseas trips, you may be familiar with the phenomenon of travel poo, wherein your stool takes on a different hue for a few days as you adjust to local ingredients. It’s far less common for the opposite to occur, but that’s what seems to be happening with Burger King’s black burgers, which have become a repeating success story in Japan.
Burger King is currently offering its darkly colored sandwich in the U.S. and the U.K., but many are reporting that while the company turned the burger’s bun black, the burger is turning their poo green. But what’s behind this transformation, and why didn’t it happen in Japan?