"What we are looking for are patterns of behavior that indicate something all terrorists have: the fear of being caught," he says.

They look for... subtle signs like vocal timbre, gestures and tiny facial movements that indicate someone is trying to disguise an emotion.

"All you know is there's an emotion being concealed. You have to find out why the emotion is occurring..."

The explanations for hiding emotions often are innocent: A traveler might be stressed out from work, worried about missing a flight or sad because a relative just died.

SPOT teams have identified about 100 people who were trying to smuggle drugs, use fake IDs and commit other crimes, but not terrorist acts.

Don't hide your emotions from the TSA. Hide nothing from the goverment. Only criminals have something to hide. We're watching.