One of the in-passing references in the first book is "truthsense". In a nutshell, it's something a few people have and almost everybody doesn't have. So the Emperor has a particular old crone hanging about who has the truthsense and who can alert him to people lying to him. Fair enough, the sort of thing you'd find anywhere from the King Arthur tales to extreme-future sci-fi.
The interesting thing here is that in later Dune books Herbert revised the talent somewhat. Now I'm probably stating the obvious that authors in general tend to tweak concepts quite a bit in a series, and even within the same book. In this case one of the later books (I've forgotten which) the truthsense is something that most people have, needing only some specific training to use. In particular the sense manifested itself differently in everybody, and so the training involved figuring out one's own way for noticing this new sense. One character wanted to comfort the person lying to her, another wanted to punch that person.
To me this somewhat rings true... I've noticed that sometimes I'll have somebody telling me something, and my reaction is a bit unusual. I'll be sort of fascinated by the way they are speaking, like I'm seeing something extremely unusual. Just about every time it's happened I don't figure it out right away, though I've learned to notice that my own reaction isn't typical and that something is amiss. This ties into my "24 hour rule" about major purchases, where I can't make any major (more than a hundred dollars or so) decision without a day to think about it. Maybe once in a while I miss a great deal, but most of the time I figure out that it wasn't such a great deal overall.
To some extent I think it relates to how my own personality causes other people to react in specific ways. To people with An Agenda To Pursue, I'm an unkown, and such people tend to react by becoming even more forceful in their delivery, as if the only way to deal with me is to sell their viewpoint extra hard.







