What's behind Wall Street whiplash and global market volatility?

Investors are bracing for more turmoil on Wall Street, as global markets suffered new declines overnight. Stocks are trading slightly higher in Britain and Germany. The Dow opens almost 470 points lower, or nearly 3 percent, after a turbulent few weeks. Financial Times' U.S. managing editor Gillian Tett joins "CBS This Morning" to discuss the market.