I could take that question.
That's exactly right, in that if we detect traces of a narcotic on the exterior of a bag, that gives us the motivation and the justification to go further. These scanners are incredibly sensitive. They're detecting nanograms of material. Nanograms doesn't mean very much to most people, but if you take a grain of salt, that's a milligram. A nanogram is a millionth of a grain of a salt. If you can see it, it's more than we need.
Really, it's just an indicator that maybe the search should go further.