I suppose you understand just how rare that must be, though.
[A small shrug.] Aside from how close they are to severe alcohol problems... all it really takes is a few drinks. Some will spill their life stories, others the skeletons in their closets. Of course, some will scale complete introversion - but those cases aren't so common. If you want to know a person's true thoughts on a situation, talking to them when they've had just the right about of liquor can really pinpoint that.