Ya'll have seen the "nude" images produced by backscatter x-ray screening.
Note the dark-colored contraband in the images above.
Now, note the dark background around the bodies above.
The blogger in the link above smuggled a small metal case in a pocket sewed on the side of his shirt through multiple TSA scanners undetected. The scanner painted the case black on a black background, rendering it invisible to the operator.
Yet again, TSA demonstrates itself to be security theater.