EMBED >More News Videos UH student pulls off impressive McDonald's ad prank

EMBED >More News Videos Bad news for those who love fries - a Harvard professor says you should only eat six fries as a proper portion.

A new promotion from Burger King sounds too good to be true.For eight days, the chain is basically giving away its iconic Whoppers for a penny.But there is a small catch: you have to help them troll their competition.In order to cash in on the one-cent sale, you have to pull into a McDonald's parking lot.All customers have to do is stop within 600 feet of the golden arches, order a Whopper on Burger King's relaunched app, then follow along as it navigates to the closest Burger King.The chain says the concept is simple, as long as you don't try to actually order a Whopper from McDonald's.The promotion, dubbed the "Whopper Detour," is good until December 12th.McDonald's has not yet commented on Burger King's ploy.