This happened many times before the WTC attack. I would go through the metal detector at the airport and then they would look at my bag with the x-ray machine but I could almost anticipate everytime that they would ask me if they could check my bag. So I always say yes and they rub this white piece of paper or cloth all over the outside of my bag and then put the paper in a machine. They always let me go after that but it happens just about everytime I fly. Anybody know what they are doing what they are testing for?
