Here are three genera, each of which gives three species.
The Normal State.
When the head is erect, it is passive and neutral.
The head inclining laterally toward the interlocutor indicates affection.
If in the inverse direction, opposite the interlocutor, sensualism is indicated. This is in fact retroaction; in the first case we love the soul, in the latter the form.
The Eccentric State.
If the head bends backward it is the passional or vehement state.
The head inclined toward the interlocutor, denotes abandon, confidence.
The head turned away from the interlocutor, denotes pride, noble or base. This is a neutral expression which says something, but not the whole.