I mentioned this in the last post re: Raj, but it really deserves a post all its own. Here's a good description I found:
the fabulous indian head bob
In India, if a person shakes their head from side to side, it means “no”. If a person nods their head up and down it means “yes”. This is all pretty familiar, no? But here there is a spectacular third possibility. It is called the Indian head bob. It is achieved by the smooth and undulating weaving of the head from side to side. A “sinuous back-and-forth-up-and-down-at-the-same-time movement, as smoothly as if the head rested on ball-bearings”.
This bob possesses a myriad of meanings. It can mean “yes”. It can mean “OK”, “Great”, or “I guess so”. It can mean “Sure” or “Eh, why not?”. If exhibited while another person is speaking, it can also mean “I'm listening” or “I understand” or “I appreciate the meaning of what you are saying, even though I don't necessarily agree with you”. I have also come to learn that it can sometimes mean "OK, you crazy American. Whatever". (http://www.aforadventure.com/headbob.html)
And to expound: (http://colorblindcupid.wordpress.com/2007/12/06/the-indian-head-bob/)
The head bob can be used to convey all kinds of messages, from the simple to complex:
Yes
No
I don’t know
Okay - I hear you. Keep going.
I’m listening
I totally disagree with that
You’re pissing me off, but I’m not ready to fight with you quite yet [otherwise known as the angry head bob]
I’m not so sure about that
I totally don’t like that idea, but I don’t want to have to give a reason why
That was kind of funny, but not funny enough to actually laugh
That wasn’t really funny, but you get a courtesy bob so you’re not embarrassed by your bad joke
I hear what you want me to do, but no way am I going to do that, so I’m just going to bob and maybe you’ll shut up about it
I’m bored now, but if I keep bobbing, the person talking to me may not notice I’m not paying attention to anything they’re saying [I so wish I could adopt this one sometimes!]
As the answer to “Why didn’t you vacuum today? I asked you to do one thing, and you didn’t vacuum? Why not?” [or insert whatever honey-do chore you like there]