Turns out, there may be an unintentional trick to Burger King's new Halloween treat.

The Halloween Whopper, a limited-edition burger available throughout the month of October, comes with a black bun to make it extra spooky.

The burger is advertised as having A1 sauce baked into the bun for extra flavor. Unfortunately, customers are saying that some ingredient in the black bun is turning their poop a vivid green color — which is causing some people to freak out a little.

The spookiest thing about Burger King's new Halloween Whopper? There's the very real chance it will turn your poop neon green. #greenpoop — Anthony J. Rapino (@AnthonyJRapino) October 2, 2015

Because it's like ... really green.

Some people have even (unfortunately) taken to posting photos of their brightly colored bowel movements to prove their point. Feel free to take a look — at your own risk — below.

Great so I eat one black bun Burger and now my pews are spooky green... #BlackBunsMatter #HalloweenPoop #greenpoop A photo posted by DuggyFlesh (@dugstrickler) on Oct 5, 2015 at 8:06am PDT

And while the bizarre side-effect has some customers seeing red (and green) ...

@BurgerKing STILL HAVING #GREENPOOP FROM YOUR #HALLOWEENWHOPPER YOU NEED TO RESPOND TO THIS BECAUSE ITS REALLY MESSED UP — Dr. Pluto A. Planet (@PLUTOAPLANET) October 1, 2015

... some customers are willing to endure mossy stool for a shot at the Halloween Whopper.

About to get my #GreenPoop on with this #HalloweenWhooper A photo posted by Arron Capone (@vandelbuster) on Oct 5, 2015 at 12:43pm PDT

Burger King has not yet responded to Mashable's request for comment.