Burger King has a big new sandwich on its menu just in time for Halloween.The fast-food chain is releasing what it calls the "Nightmare King" next week.The spooky sandwich is a quarter pound of flame-grilled beef, with a chicken fillet, American cheese, bacon, mayonnaise and onion.What probably grabs the most attention is the fact that it's topped off with a green sesame seed bun.Officials with Burger King say this sandwich is clinically proven to induce nightmares. In an online advertisement seen in USA Today for the "Nightmare King," Burger King claims to have partnered with Paramount Trials and Florida Sleep & Neuro Diagnostic Services, inc. on a scientific study over ten nights with 100 participants. After eating the new burger, participants claim nightmares increase by 3.5 times, according to the results.The "Nightmare King" sells for $6.39, and will be available starting Monday through November 1.