By now, many travelers have come to realize that officers from the Transportation Security Administration aren't just confiscating their liquids and occasionally patting them down. They're also sizing up passengers for signs of suspicious behavior, such as excess anxiety or sweating. Known as the Screening Passengers by Observation Technique, or Spot, the program was put in place to nab terrorists and is now used at roughly a third of U.S. airports. After nine years, government studies show that it's turned out to be an effective tool for sniffing out alleged criminals—just not the ones it was intended to catch. So amid criticism from civil liberties advocates, the U.S. Department of Homeland Security has brought in consultants to revisit the program.