I love people watching. After all, for a theatre director, this is how you learn the grammar and syntax of human interaction. Little moments of physical behaviour provide the director with passages of movement that can be choreographed into a stage picture to underline the intentions of the characters. The audience will probably recognise these little elements and a director can also play with them to contradict their dialogue to produce little tropes and moments of unease.
Two examples which I have noticed in the past couple of days: At a gallery for a private view night. Most people arrived in pairs or singly, As they took up positions around the gallery, the singletons would join the pairs as they recognised friends and acquaintances. One of the original pair would eventually leave and another wanderer would join the group. Thus, over the course of the evening, the predominant group size was the trio but with the members continually changing. These little groups would hold more or less the same position in the room despite the everchanginging personnel.
Secondly: A pedestrian precinct observed from above. The patterns that passers by made were a complicated series of swirling curves and arabesques as individuals moved through the crowd. Even those with an apparent sense of purpose did not make a straight line but a series of sweeping zigzags. There are no straight lines in human interactions.