Social media has been abuzz recently about Burger King's new black Halloween Whopper, but it's not because of its burnt looking black buns. Apparently, this Whopper turns poop green, and those who eat it even just once have bright #GreenPoop for up to several days, according to the Daily Mail.

The Halloween Whopper in the U.S. is not prepared the same way as the black Whopper in Japan, which uses bamboo charcoal and squid ink for its color. A spokesperson for the burger chain said that the new black buns have A.1. steak sauce baked into them, giving them their black color and some added flavor. The black buns reportedly had less than one percent food dye in them.

"We tailored the flavor of the black bun to the American palate with A.1. sauce, a flavor this country loves, and we're delivering it in a way that's never been done before by baking it into the bun," Eric Hirschhorn, chief marketing officer for Burger King Brand North America, told ABC News. "It may look Japanese but it tastes like America."

However, many people are not convinced that the steak sauce was responsible for the buns' black color, especially when they ended up having bright green stools after eating the Halloween Whopper. So what could be in this Whopper that turns poop green?

Some speculate that it could indeed be food dye. A dark green food dye would make the buns look darker, and it is also known to cause poop to turn bright green. Other suspects are purple and blue food dyes because both are dark colored and could help achieve a burnt look for the buns, and they are also known to result in bright green stools, The Washington Post reported.

Burger King has not offered an official explanation for how the Halloween Whopper causes #greenpoop. Meanwhile, the tweets continue.

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