Bowel movements beware...
Burger King's Halloween burger is providing a serious fright for customers, who have complained that it's turning their poo a ghoulish green.
People have taken to social media to moan (and sometimes jest) about the fast food joint's Halloween Whopper with the hashtag #GreenPoo.
The burger in question comprises flame-grilled beef with melted cheese, tomatoes, lettuce, mayonnaise, pickles, white onions and a black-coloured bun topped with sesame seeds.
It is available to buy in the UK and US throughout October.
The spooky-looking bun, which gets its colouring from A.1. Sauce, is believed to be the poopetrator.
The company told ABC News that the black bun contains less than 1% food dye.
The most common reason for green poo is a dietary habit or change, such as being on a diet rich in dark green vegetables. But, according to Healthline, it can also be down to food colouring which doesn't get processed properly.
HuffPost UK has since reached out to Burger King for comment.