Burger King began serving beefless Whoppers on Monday--and it was no April Fools' Day joke. According toThe New York Times, the company began serving the Impossible Whopper, which features plant-based patties instead of the traditional beef ones. The vegetarian patty is made by Silicon Valley start-up Impossible Foods. The fast food chain doesn't expect anyone to be asking, "Where's the beef?," as Burger King's chief marketing officer Fernando Machado claims, "People on my team who know the Whopper inside and out, they try it and they struggle to differentiate which is which." The Impossible Whopper is currently only available at St. Louis area locations, but the company hopes to expand across the country if everything goes well.