The people of Yemen can hear destruction before it arrives. In cities, towns and villages across this country, which hangs off the southern end of the Arabian Peninsula, the air buzzes with the sound of American drones flying overhead. The sound is a constant and terrible reminder: a robot plane, acting on secret intelligence, may calculate that the man across from you at the coffee shop, or the acquaintance with whom you've shared a passing word on the street, is an Al Qaeda operative. This intelligence may be accurate or it may not, but it doesn't matter. If you are in the wrong place at the wrong time, the chaotic buzzing above sharpens into the death-herald of an incoming missile.