In India, people have a variety of head movements which are meant to convey certain meanings, intentions, or feelings. Some are more ambiguous than others so be cautious in your conclusions!
Bobble side to side: Tipping the head from side to side (left ear toward left shoulder, then right ear toward right"”back and forth) means "yes," "ok," "good" or "No, but I don't want to tell you that." (A "no" bobble is often accompanied by a frown or apologetic smile.)
It's also a polite, encouraging gesture for listening to someone, like saying, "uh huh, uh huh," meaning "I understand" (whether the person does or not). The quicker and more decisive the movement, the more positive the meaning.
This can also be used to convey "thank you," which is not so frequently verbalized, and as a nonverbal "hello" when accompanied by a smile and slight raise of the eyebrows.
Horizontal side to side: Turning the head from side to side (chin toward left shoulder, then toward right"”back and forth) means "no." A quick one usually means a definite "no." In South India, however, a gentle prolonged back and forth can indicate admiration.
Nodding: Tipping the head forward down and up usually means "yes," but may also mean "no." One quick nod (or sideways tilt), accompanied by a smile, is used to say, "Hi! How's it going?" If you actually ask this question instead of using the nonverbal gesture, you may be subjected to a painfully lengthy answer.
One quick nod down means, "Come here." A quick nod up means "Go away."
Wobble: Tipping the head like the vertical side to side, but with more of a sway in it, a looser chin movement, means "maybe yes, maybe no." This looks a lot like the vertical side to side, so you really have to look closely for that little extra loose wobble. Even when you have identified it, you still don't know for sure what it means. You do, however, know it doesn't mean a definite yes or no, and can often indicate some hesitation when performed slowly.
If all this seems confusing, you might enjoy this amuzing YouTube clip. However, the correct interpretation isn't quite as cut and dried as they make it sound, but it's a good starting point.
Indians, in general, prefer a rather indirect, implicit style of communication in interpersonal relationships. Being too direct, clear, or honest, especially where feelings could be hurt can harm relationships. Being too explicit among friends, such as frequently saying "thank you," gives the feeling of less intimacy, and consequently less trust"¦