STRONG selling fuelled by a minor rout in Henderson Land Development shares yesterday wiped 95 points off the December Hang Seng Index future, taking the contract to below the 10,000-point level. The contract closed at 9,910, a premium of 11 points over the cash index. January futures also fell 95 points to 9,955, a premium of 56 points to cash. Further weakness in the cash market is expected today. If selling is sustained, bulls which have been going long in both December and January might get a bit jittery. Conspiracy theorists say big property developers are shorting the market. Volume yesterday was relatively modest at 16,624 contracts. There were 15,523 contracts traded in December and 1,101 in January. Index option traders seemed to be of the opinion that the bulls had had their fun, after two days with December above 10,000. Now, the bears are due to take over. Heavy premium selling took the front-month implied volatility to 17.75 per cent. Jardine Fleming said this encouraged some investors to go long volatility. 'The December 10,000 and 10,400 calls were bought on a delta-hedged basis,' the brokerage said. Bears sold December 9,600 calls when the future consolidated around 10,020 in the morning, it said. Delta is a key measure of rate of change of an option price in relation to the rate of change in the price of the underlying asset, in this case the cash index. Delta hedging involves covering the position to hedge against volatile movements up or down. There were 2,981 lots traded in index options, while 3,227 HSBC stock options and 1,031 Cheung Kong options were dealt. Today will be a fairly critical one in terms of sorting out a trading trend for the short term until the United States Federal Open Market Committee meeting on December 19. Although index options look relatively attractive, on such apparently low implied volatility, some chastened bulls might be keen to cover aggressive long positions. They can either buy puts or sell calls. Investors are focusing on December 19 because a land auction on that day is also expected to set the tempo of domestic equity investment sentiment.