Terrorism penetrates the psyche by being unpredictable. Terrorists rely not only on the element of surprise but also on a second-level uncertainty to strike so deep: The difficulty of knowing exactly who the terrorist might be. Background is no guide. Many of the 9-11 plotters had tertiary educations. Others, like the self-starting (and foiled) millennium bomber and former petty thief Ahmed Ressam, came from the social margins. Ethnic profiling, proposed again recently by New York Representative Peter King, hardly works. The July 2005 London attackers and the recent High Wycombe arrestees both defied racial stereotypes. Any halfway calculating terrorist group, moreover, will simply work around ethnic profiling.