There is a scene in Polish crime movie "Psy" (great movie BTW, http://www.imdb.com/title/tt0105185/), where a bad guy answers this question by saying: "Noone ever lied with a car battery connected to his balls"
http://en.wikipedia.org/wiki/Effectiveness_of_torture_for_in...
[2] Torture Has a Long History ... of Not Working
http://www.livescience.com/4651-torture-long-history-working...