One time, in France, after I was locked for about 1.5 hs in a room answering question and my luggage disassemble completely. When they realize that everything was ok and got relaxed I asked why I was picked.
And they said to me, well, the first thing you did was to look where the cameras were, then you stay in the corner where the cameras could barely reach you and stay staring a fix point without moving your eyes until you picked your luggage.
Ok, I am an electronic engineer, I am in the security business so I guess that my behaviour is expectable, I didn't say that though.