The eyes tell where the body wants to be, and when the mind is fully engaged on the presentation, the focus will be on the speaker rather then what is going on around them. Looking away rarely happens with someone who is completely engrossed in a conversation unless they do so to concentrate. Our eyes become fixated at the exclusion of anything else in the room and our ears become finely tuned to the voice of the broadcaster. When completely engaged, there is a fear of missing something important.
An interested listener is focused on the entire person, their gestures, voice tone and the information delivered. An attentive listener is directed, having their bodies oriented toward the speaker, their arms open and apart willing to take information in, their legs will be crossed or open but aimed at the speaker, their head might be cocked to the side at forty five degrees showing interest, and any information they add will be appropriate to the given subject rather than off topic. There will be times, when a fully attentive person will look away, down or about the room, but these ganders are few and brief, with the primary attention placed back on the speaker.