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A depiction of a man nodding
A nod of the head is a gesture in which the head is tilted in alternating up and down arcs along the sagittal plane. In many cultures, it is most commonly, but not universally, used to indicate agreement, acceptance, or acknowledgment.
Nodding to indicate acceptance 
Different cultures assign different meanings to the gesture. Nodding to indicate "yes" is widespread, and appears in a large number of diverse cultural and linguistic groups. Areas in which nodding generally takes this meaning include the Indian subcontinent (note that the head bobble also shows agreement there), Iran, Southeast Asia, Western Europe, Latin America and North America. Nodding may also be used as a sign of recognition in some areas. Nodding is also used to show respect. Insult can be inferred if it is not returned in kind.
There are varying theories as to why nodding is so frequently used to mean "yes". One simple theory is that it is a form of bowing, indicating that one is prepared to accept what another person is saying or requesting. It has also been stated that babies, when hungry, search for milk by moving their heads vertically, but decline milk by turning their head from side to side.
An early survey of nodding and other gestures was The Expression of the Emotions in Man and Animals, written by Charles Darwin in 1872. Darwin wrote to missionaries in many parts of the world asking for information on local gestures, and concluded that nodding for "yes" was common to many different groups.
Nod of acknowledgment 
The nod of acknowledgment, used as a form of greeting, is a slight nod of the head.
Nodding syndrome 
Nodding is also a symptom of a yet unexplained disease. It affects mostly children under 15, and was first documented in Tanzania in 1962.
See also 
External links