nod
Nodding, is a kind of neck as the base point, the head up and down the human ritual, in the vast majority of human society that "yes", that is, agree, accept or understand. But in a few cultures (such as Albania, Bulgaria, Sri Lanka), nodding is "no". In 1872, Charles Darwin conducted a preliminary study of "nodding" in his book "The Expression of the Emotions in Man and Animals". He communicated with missionaries around the world that almost all of the cultures were "nodding" and "yes". The source of this ritual is not conclusive, there is a saying that this is from the human infant instinct, when the human baby to find the mother's milk, often unconsciously make nodding action, and when it does not need milk, then Will swing the head. Another said that the nod is bowed to the simplified type. ...