Head on, means passive listening for example, head slightly tilted shows moderate interest and head at its maximum forty-five degrees shows full immersion. A teacher might see variations across his audience, and also across the subject matter. Head tilting is not an all or nothing phenomenon. This makes it easy to measure the success of a presentation nonverbally and tweak it as necessary.
Dogs also tilt their head, usually by engaging them in human conversations, so the root of this mechanism could simply be the state of being confusion. The head tilt is also a submissive gesture as it exposes the neck making it vulnerable to attack. One of the more prominent courtship displays is the exposed neck, and when done by women, is particularly alluring. This is examined in a later chapter.