I observed an almost surreal event when I was a business student.

At the front of the classroom, an entrepreneur was practicing a pitch he would make later to venture capital firms. Specifically, he was talking about a technology his firm had developed, a respirator which had the potential to save the lives of many infants.

When he talked about the potentially great financial returns, the audience, made up of business students, sat back passively. But when he talked about getting babies through critical moments with his respirators, every single person in the classroom sat up, alert and fully focused.

As he went back and forth between stories of saving babies and talking about financial results, almost every student in the classroom moved with him. And what's more, it seemed the students' unconscious body movements had been carefully choreographed.

We sat up together when the entrepreneur talked about saving babies, and we sat back in unison when he discussed the numbers. And, by the way, I did it too until I become aware of how we were responding as a group.

Since that event I've been a firm believer in body language, which is the idea that people unconsciously show what they're feeling or thinking through gestures or body movements.

As you know, the art of interpreting body language is hardly a science. But, we do know a few basics that can help us read the emotions of others. A few examples follow.

Crossed arms, as almost every salesperson knows, means the person on the other side of the table is defensive or not receptive. On the other hand, if that person leans forward and keeps his or her eyes on you, then you do have a receptive listener.

If you watch novice speakers, you'll probably notice how they keep their arms close to their bodies, indicating a lack of confidence. As they get more practice speaking in public, you'll see their arms move away from their sides and become active tools for conveying messages.

Arms wide open indicate trust and openness, as do open hands, while arms held high above the head show a sense of victory, and clenched hands indicate anger.

Curiously, one of the most difficult interpretations of body language involves lying. Researchers have probably spent more time on this aspect of body language than any other. And their conclusions? The only surefire way to know if another person is lying is to observe very small and fast wrinklings of the brow.

If you haven't yet spent much time studying body language, I recommend that you add it to your to-do list for communication development. It's invaluable not only for speaking and listening, but also for negotiating and leading.