Action;
[ His brows arch a bit as he nods, even as he finds himself... explaining. Because that is what he does. ]
Though I have had limited experience with identifying emotional states which are more elusive and multifaceted, I have studied the specific combination of the more readily identifiable responses which I have experienced and compared these responses with those I have seen described in both literary and psychological sources.
[ All of which is a very long-winded way of saying... ]
It is the only possible conclusion which I have found.