If a pair of Transportation Security Administration officers strolling by a Sea-Tac Airport ticket counter wish you happy holidays and ask where you're traveling, it might be more than just Christmas spirit. Travelers at Sea-Tac and dozens of other major airports across America are being scrutinized by teams of TSA behavior-detection officers specially trained to discern the subtlest suspicious behaviors. TSA officials will not reveal specific behaviors identified by the program -- called SPOT (Screening Passengers by Observation Technique) -- that are considered indicators of possible terrorist intent. But a central task is to recognize microfacial expressions -- a flash...