[yaps8]

I wonder how they are trained to differentiate between someone who is hiding something and someone who is uncomfortable because they have been in a 10 hours flight, barely slept, have not been speaking english for months and are anxious to be suspected for nothing.

[throwawaysocks]

Ostensibly facial ticks or whatever.

Actually country of origin and maybe skin color / attire.

That's the function of pseudo-science bullshit -- you can ignore civil liberties and pretend you're not.