When stocks fall, investors usually buy bonds. Not this time. : Yet during the stock market mayhem of the past two weeks, not even safe U.S. Treasury bonds were spared. The Dow plunged 2,400 points, or 9%, between January 26 and February 9 as investors fretted about the threat of inflation. But in a twist, investors sold bonds, too. The yield on the 10-year U.S. Treasury note, which moves opposite the price spiked from 2.62% to 2.85%. Then it inched higher again on Monday because investors kept selling bonds, even while they drove the Dow up 400 points.