Back before the era of cellular phones, I read an article written by a student of human nature who described two men approaching each other on the sidewalk. They look at each other as they get closer, probably to discern whether there is a threat. When they get within a certain distance, and no threat has been perceived, they both look down at the path. It was described as being similar to motorists shifting their headlights from high beam to low beam. Do some people watching and see if that description is still true.