Another thing is, if you notice, when people are actually talking, some of them tend to look as if they're thinking of what to say. Well if they are looking up towards one part of their brain, it's because they're searching their memory for more details on whatever, so they're telling the truth. And if they're looking up towards the other half of their brain(associated with creativity), then they are trying to invent something to say, so they are lying!!!
I seem to have forgotten now which side's which, sorry guys, but if you take note, next time you're trying to suss someone out, you'll figure it out for yourself.