Human beings are genetically programmed to look for facial and behavioral cues and to quickly understand their meaning. We see someone gesture and automatically make a judgment about the intention of that gesture. The gesture and our interpretation of its meaning can profoundly affect team dynamics.
And we've been making these judgments for a long, long time. As a species, we knew how to win friends and influence people - or avoid/placate/confront those we couldn't befriend - long before we knew how to use words.