I don't know about you but I have this tendency to wobble my head when I speak with my Indian friends.
I : So you're bringing curry chicken for potluck.
Friend : Yes (wobble his head)
I : Good (wobble my head)
Even on the phone, when my friends can't see me, I go wobbling.
I : Can you please give me M's phone no.
Friend : Sorry I don't have it. (probably wobbled her head)
I : You don't have it? It's allright. (wobble)
Here's the link to an interesting article on the wobble.