The most common use of the head wobble is to respond in the affirmative. For example,if you ask someone if the train is going to you destination and they wobble their head in reply, it means "yes". The head wobble is also often used as a sign that what's being said is understood. For example,if you tell someone you'll meet them at a certain place at 5 o'clock and they wobble their head at you, it means that it's fine and they'll be there.