We have moved from head shaking to grunting. Rickshaw drivers, boaters and pedestrians alike tend to address each other through a series of grunts. It goes something like this:
1st man in lungy approaches and grunts at on coming man.
2nd man grunts back.
1st man ends the conversation with a knowing “Ahhhh” and a nod.
Much like the head shake, not sure if this is positive, negative or simply neutral, but in the end they seem satisfied.