Having the hands deep in a pocket or behind the back can be a sign of aggression or passive threat, and our evolutionary history tells us that someone who is hiding something is probably not hiding a bouquet of flowers. But if they are, why take the risk! Showing open palms, facing up, or the “palm flash” is essentially what would have happened thousands of years ago when two foreign tribes met.
“Palm down displays” such as by placing hands face down on a table or standing head on and leaning with the fingertips spread to anchor the body shows emphatically that a position is held confidently. While conversing on a topic, we should therefore expect both palms up and palms down as opinions are either offered with reservation or presented with conviction. The rule of thumb is that palms down “telling”, while palms up, “offering.”