Last September, Burger King introduced a sandwich with black cheese and a black bun in Japan. The Japanese version was flavored and colored with squid ink and charcoal (yum), but when BK brought the idea Stateside, they kept things American by leaving the cheese yellow and flavoring the bun by baking it in A.1. Steak Sauce. The Halloween Whopper debuted Stateside on September 28, but diners have discovered that the black bun is doing scary things to their insides. Mashable reports that people are tweeting about their "neon green" or "spooky green" poop, with some going so far as to post toilet-bowl pictures, just in case no one believes them.
A scan of #GreenPoop tweets reveals four archetypes: the matter-of-fact, the mildly grossed out, the intrigued, and the enraged. While the company doesn't list the burger's ingredients on its site (no chain really does), it does include this statement on the full nutrition facts list:
The flavoring and food colorings used to color the HA.1.®LOWEEN WHOPPER® black bun in the US, are commonly used in the industry and within the safe and Acceptable Daily Intake (ADI) approved by the Food and Drug Administration (FDA).
Some would disagree about "acceptable." But as anyone who's eaten beets and then texted a friend in panic knows, even foods without added dye can make your poop change to terrifying colors. Trick or treat!