Shares in Wal-Mart de Mexico y Centroamerica plummeted this week as allegations the company bribed officials to speed up store openings prompted many shareholders to offload the stock at a rate of knots. Meanwhile, concern that US regulators will pursue action against parent company Wal-Mart Stores for violations of the Foreign Corrupt Practices Act could have some far-reaching consequences for the world's largest retailer. Katy Askew reports.