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.
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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.
How was my turd after eating the #HalloweenWhopper ?#GreenPoop pic.twitter.com/tAL22JHPwY— Rocko Ostolaza (@rockoide) October 5, 2015
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.
This is what happens when you eat @BurgerKing #HalloweenWhopper #GreenPoop pic.twitter.com/EeoxUYzAsa— FPlus (@FPlusPS3) October 1, 2015
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.