Centex (CTX, news, chart, volatility) is seeing six times normal trading volume, with help from a large block of more than 24,000 January 15 puts traded above the offer for $3.00 a contract. With open interest of 7,531, this appears to be an opening buy order. 10,000 of the October 15 puts traded on the bid for 80 cents a contract and taken together activity in these two contracts might be rolling of protective puts from October to January. Shares of the homebuilder are down $1.00 to $16.30.