The scariest part of Burger King’s Halloween Whopper doesn’t happen until after you eat it.
Something in the burger’s pitch-black bun turns eaters’ poop a ghastly bright green — sometimes for as long as three days.
“The Halloween Whopper turns your poop green,” tweeted John Kritzman. “And not even sickly green. Like cartoon green. Comical green.”
Not everybody was amused by the frightening after-effects of the Halloween treat, with some even vowing to never eat the burger again.
“Yesterday I had the Halloween Whopper,” added Daniel Rodriguez. “Today my poop is green. Yesterday was the last time I’ll have the Halloween Whopper.”
It is unclear what ingredients in the black Whopper turn stool such a haunting color, but a spokesperson for the fast food giant told ABC news that the bun contains less than 1% food dye.
The spokesperson added that black color comes from the “smoky black pepper flavor of A.1. (sauce) baked into the bun.”
Certain dyes, such as Green #3, are known to turn stool green. Also, poop can appear green if bile doesn’t break down food quickly enough.
Burger King doesn’t specifically list the dye used in the burger, only stating that all of the food colorings used “are commonly used in the industry and … approved by the Food and Drug Administration.”
There have been reports that the Halloween Whopper turns your poop green. I can confirm those reports.
— Martin Ryder (@itsmartinryder) October 1, 2015
The restaurant chain first introduced the burger in Japan last year, using bamboo charcoal to give the bun its black hue. The American equivalent does not use bamboo charcoal.
The stunning effects from eating the sandwich caused a significant uproar on social media, but not everyone was disgusted by the unnatural color of their post-Whopper stool.
“Took like three days for my poop to stop being green, but was totally worth it,” tweeted Hunter Stanton.