Very recently, social psychologists have started to analyse walking a skilled performance. The fundamental problem is navigational; do we manage to avoid collisions, the aid of the motorist's horns and hand-signals, etc? As we survey the oncoming pedestrian traffic, we must first decide it is organised. Who is walking together and alone? Convention dictates that the solitary must acknowledge the unity of an approaching group by walking round it; to otherwise is considered rude or even provocative. If the group is big to permit this, it usually breaks into smaller units to the lone walker to pass it without the rules. People who are walking together demonstrate the fact in a number of ways. They may be hands or talking to other, but the reliable sign of togetherness is deliberately maintained proximity. This is most obvious when an obstacle is encountered or a corner ; by adjusting their pace to re-establish contact others, pedestrians it clear that they are walking and not merely the same pavement the same speed.