The other questions though, again, is how does playing 20 questions benefit the passenger?

As far as I've heard, regardless of the performance during 20 questions, all passengers are still required to complete body scanning or magnetometer screening as well as to have their carryons scanned and possibly hand searched and/or swabbed for explosives toxicology; and if there is any question about the results of their body scanning or magnetometer screening, they are still subject to wanding and/or patdown.

So what is to be gained by 20 questions as currently proposed?

Is there a shred of evidence that the 20 questions procedure raises the sensitivity of detecting weapons or explosives compared to body scanning etc alone -- in trying to identify individuals who might have weapons concealed in body cavities that cannot be identified by the other routine screening techniques, for instance?

It only begins to make some kind of sense if a favorable behavioral profile generated during the interrogation would allow the prospective passenger to be selected out of one or more of the other screening steps, or if there is evidence that using the behavioral profiling with the interrogation in combination with the other screening measures increases the overall screening sensitivity.