If Burger King’s black A.1 Halloween burger wasn’t freaky enough just to look at, what happens after you eat it might give you a real fright.

The new sandwich, which debuted Sept. 28, is reportedly turning some people's excrement a bright green color.

Twitter users have been tweeting about their experiences, with some brave users even adding photographic evidence.

We'll spare you the graphic images, but a quick Twitter search will give you an idea of what some are claiming.

While some appear to be turned off by the side effect, at least one Twitter user was excited about the prospect of having a a green colored bowel movement:

According to Burger King’s website, the Whopper bun gets its dark look with the help of the popular steak sauce, as well as food colorings including D&C Red #40, Molasses Powder, and FD&C Blue #1.

We reached out to Burger King about why these burgers are one color going in and another going out-- and are still awaiting comment.

But when the burger chain released the burger, a representative told ABC News that the black bun contains less than 1 percent food dye.

Dr. Robert Glatter, an emergency care physician at Lenox Hill Hospital in New York City, told FoxNews.com that many common synthetic dyes, including D&C Red #40 and FD&C Blue #1 "are generally not able to be broken down or absorbed by the body so they end up coming out in the stool."

He said that burger lovers shouldn't be alarmed and noted that the Food and Drug Administration considers these dyes safe for public consumption. Also, similar reactions occur when people eat natural foods like beets or consume of large amounts green vegetables.

"That said, I advise eating more fruits and vegetables and foods which are free of additives whenever possible," he said, adding that brightly colored stool lasting more than few days could mean something else, so check with your physician.

But if you're thinking about trying the black Whopper, just be prepared for the extra Halloween surprise.