The questions vary from person to person and will depend on your pysch profile. Some people they are friendly too others they give a real hard time. Had a mate leave the interview a shattered man after the grilling he copped!
They make up stuff, cut you off, have a go at you, accuse you of lying, play games etc etc They also give you some standard interview questiosn, AIP, Aerodynamics, QF stuff.
The flaw in behaviour based interviews is that if you know what they are playing at then you just play along and give the answer that they want regardless of what you would really do. You also taint all your answers to put you in the best light. You don't need to tell them everything just what benefits you. Bit like selling a car really! Behaviour based interviews really only work if the candidate is unsuspecting so why the hell they use them is beyond me.
I have heard however that the argument for behaviour based system is that if a candidate is willing to modify their behaviour to fit what the organisation wants then that's considered a good thing!! So in theory you could employ a pyschpath who modifys his behaviour for the interview then becomes something else once he's in!