There’s a lot of misinformation about body language sloshing around in the information ocean that is the Internet. Perhaps the most fundamental wrong-headed idea is that you can reliably read the body language of strangers simply by knowing a few universal ‘tells’.  Wouldn’t it be nice if that were the case?  Then we could join a high-stakes poker game, watch for the tells, and rake in the big hands from strangers because we would be able to discern between the bluffs and the winning cards.  Sadly, and this is the bad news:  body language doesn’t work that way.  It’s multi-determined, for the most part, meaning that a gesture might have several motivations behind it.  I might cross my arms when I’m feeling defensive, for example, but also when I’m cold, or tired, or I’m overwhelmed with information and trying to protect myself from having to take in anything more.

The good news is that there are a couple of ways in which reading body language is relatively reliable.

First, most humans are reasonably good at reading the signals of people that they know well – long-time colleagues, friends, family – especially when they are moved by a strong emotion.  So, for example, when your spouse runs into the house excited about a raise, you can reliably pick up that something (good) is going on.  That’s because you know how that person normally acts, and thus spotting a variation from the norm is relatively easy and reliable.

Second, the autonomic actions of the human eye can tell us a good deal, most of it reliable.  The hard part here, of course, is getting close enough to be able to pick up on subtle changes in the eye without appearing to be staring.  Staring hard at someone else’s eyes might get you relatively reliable body language signaling discomfort, but how useful is that, really?

So, what do the eyes tell us?  Broadly speaking, our pupils dilate when we like something we see – an attractive potential mate, a bowl of our favorite ice cream, or four aces.  And they contract when we confront something we don’t like – a pile of dirty dishes, pistachio ice cream, or a 10-high nothing happening hand.

Another revelation the human eye can reliably make is when we’re trying to decide between a couple of choices.  Then, our eyes tend to dart faster around the locale of the option we’re going to pick, jumping from one point to another, as we close in on that decision.  These jumps of the eye are known as saccades, and their speed and destination reliably indicate our choices.  But of course, that’s not all there is to it.

The harder we think, the more our pupils dilate.  When it gets too much, when we get overloaded with thought, our pupils will start to constrict.  If something retains our interest, however, then our pupils tend to stay dilated.  And pupil movement can indicate a bit about personality:  the more our pupils dart around, generally, the more impulsive we tend to be.

What does all of it add up to, considering that it’s hard to discern something as subtle as pupil dilation or eye movement?  There’s some indication in the research that we can pick up those eye movements and pupil dilations unconsciously, even if we are not consciously aware of them.  So perhaps the best thing to do is to (not too awkwardly) watch the other person, and then see what kind of a vibe you get.  But I wouldn’t bet a fortune on your feeling; lots of body language research suggests that our ability to read others is no better than chance, at least when it comes to spotting a liar.

And besides, a lot of high-stakes poker players wear dark glasses.