Here is an example:
My brother has a Titanium rod that runs from his knee to his ankle in his leg. When he went through security, he set off the alarm. The female officer made him step aside. He told her of the rod in his leg. She ran her hand scanner along his leg and it sounded. She waved the scanner around the rest of his body and it never made a peep. Every time she ran it down his leg, it sounded from his knee to his ankle.
This would tend to backup what and where he told her the rod is and why it is there.
She made him assume the position and began a hand frisk. She felt the need to frisk his entire body, groping his privates so thoroughly he though she was doing a medical exam.
Now, since the metal was obviously in his lower leg and a frisk of his lower leg did not turn up any "contraband", and pulling his pant leg up and having her scan his bare leg proved the metal was INSIDE his leg, why the full body frisk ... and why all the genital groping?
This is what some people experience and what gets mentioned more then the "good" experiences.