use of "τσου" is optional and reserved only for heavy emphasis on the "no". The emphasis on the raised eyebrows and the rolling up of the eyes is such, that the actual nod of the head upwards has ended up being of secondary importance. A person can denote "no" by simply raising their eyebrows and rolling up their eyes, with the head staying completely still. As greeting Nodding can also be used as a form of nonverbal greeting or acknowledgement of another's presence; in this context, it is essentially an especially mild form of bowing, with just enough movement to show a degree of respect without additional formality. This includes the traditional downwards nod, or the upwards nod (which is more informal and usually used among friends or subordinates). To increase the formality, the downwards nod may also be accompanied by a suitable verbal greeting. In America, men often greet other men with whom they make eye contact using a nod. This greeting is often referred to as "the nod". It has been claimed that "many men feel a great deal can be intuited from the gesture [...] replete with all sorts of little nuances." Nodding syndrome Nodding is also a symptom of nodding disease, an as-of-yet unexplained disease. It affects mostly children under 15, and was first documented in Tanzania in 1962. See also Head bobble Head shake Physical distancing References External links The Straight Dope Imponderables Head gestures Human head and neck