The person will shake their head as an emphasis of articulation. These head shakes may be brief and jittery, or long and accentuated. There is often a sharp, angular halt at the end of each head shake, denoting the finality of judgment. This signal is not necessarily related to the expression of disapproval; it may just as easily relay agreement.
This signal reveals a psychology that is presently relaying their convictions and beliefs to others; pushing their paradigm out toward the audience. Their psyche is, consciously or unconsciously, aiming to persuade, move and change the opinions (and ultimately actions) of their audience. The focus of their mind is presently concerned with the practical and logistical implications of the topic.