Wal-Mart is expanding its fleet of smaller-format stores, called Neighborhood Markets. The Markets, which are one fifth of the size of Wal-Mart Supercenters, pose a major threat to traditional supermarkets like Whole Foods, Kroger, and Trader Joe's, according to Moody's analysts. on "The advantages of the Neighborhood Market concept will be difficult to beat back," Moody's Vice President Charles O'Shea said in a recent note to clients.