Originally Posted by
goalie
secondary (i.e. additional/enhanced) screening is what the tsa does to you when....
- you have an unresolved alarm upon going thru the wtmd and "win" a full body pat down (with or without an explosives test swab of your palms and/or shoes)
- there is an item in your bag that the tso cannot determine what it is at the x-ray and they must do a bag search
- either or both of the above "when they feel like it" to justify it being totally random*
That just about covers it, except the bolded part should read
whether or not you have an unresolved alarm 
That's what I was told by TSA when they picked e for secondary even though I did nor alarm. "We can check you out even if you trip an alarm:.
Originally Posted by
goalie
for u.s. customs, it all depends upon your nationality as to what if anything you are asked. just be up front with nothing to hide and you'll be fine.
In another thread about CBP a CBP personnel pointed out it's more important to have a credible (to the CBP officer) story than a truthful story.
. Whether your story is credible o the CBP or not, you guessed it, depends on the appearance of your nationality.
Originally Posted by
goalie
*if you have a muslim sounding name, appear (n.b. appear) to be "brown skinned and/or are wearing a turban, it is considered a
random selection
In other words, it doesn't matter what you say. Your story is lousy and not worthy of being credible.