Snapping two days of gains, the Sensex at the Bombay Stock Exchange dropped 57 points, or 0.4 percent, to 15,883, on profit-booking by investors, after very volatile trade, today. The Sensex had rallied more than 480 points in the past two trading sessions. The Nifty at the National Stock Exchange fell 16 points, or 0.3 percent, to 4,750. Stock markets in Japan, China, Hong Kong, South Korea and Singapore ended mixed.