High-frequency trading (HFT) is when sophisticated computerized algorithms buy and sell stocks at speeds as fast as a nanosecond, hundreds of thousands of times a day. We talked to Sal Arnuk of Themis Trading. Every day, he and his guys trade millions of shares for pension funds, mutual funds and other firms that manage your money. For Sal, high-frequency traders are his worst enemy — a faceless computer who can beat him to every trade. And the Daily Pulse is down today on news that, barring a minor miracle, 2011 will be an all-time low for new-home sales.