Traditionally, you wash your butt off with your left hand after shitting, and you eat with your right. And never the twain shall meet. However, I’ve discovered that, even if you are wiping with paper (I’m a water fan myself), and eating with utensils, the organizations of the hands into one-clean, one-dirty is a profoundly useful innovation. Particularly in a country so full of pernicious dirt. By establishing a clear rule, you effectively quarantine disease to your left hand. The quarantine can be so complete that you may wash your hand seperately, doing the one-hand-wash for each.

Common activities for your left hand: touching a flusher in a public toilet, brushing dirt or rain off your seat, petting dogs, cleaning your shoe, picking things up off the ground, pushing open suspicious doors. Common activities for your right hand: holding utensils, holding street food, holding your tooth brush, shaking hands (Shaking hands, a notorious spreader of disease, is probably safer if everyone is following the same rule. Which they are in India, more or less.), eating candy, picking your teeth, etc. I dare say that if such a custom were adopted in the U.S., it would probably cut down on the spread of germs.