While virtually all of my first visit to India was profoundly disorienting, one of the strangest differences I noticed was the Indian head shake. If you’ve been to India, you’ve seen it (and if you’re an Indian, you’ve almost certainly done it): it’s a sort of swivel/shake/bobble that’s not particularly easy for the untrained neck to replicate. No matter how many people I asked, though, I never got a clear answer to what it meant — Is it a yes? A no? A maybe? An, “I didn’t understand a word of what you just said”?
All of them were plausible. It turns out, there are different categories of the head shakes, and Meenfriedchikencurry has the explanation for all of them. Now I can go back to India and be just slightly less confused.