BSE Sensex on the starting day turned weak, after two back-to-back sessions of gains as the benchmark Sensex cracked below 31,000-mark after investors indulged in profit-booking. The 30-share index slipped below the 31,000-mark by falling 158.31 points, or 0.51 per cent, to 30,869.90 as profit-booking set in recent gainers. According to the Brokers said,"emergence of selling by participants at record levels amid discouraging fourth quarterly earnings by some bluechip companies dampened sentiments." US Dow Jones Industrial Average ended 0.01 % inferior on Friday. Also Read: Sensex and Nifty shot up in early trade today Sensex recovers 123 points in trade today Sensex also slips 85 pts in early trade