Cantus always seems to be gazing off into the distance. It seems to me that even when he's talking to someone he's not really looking at them. I was wondering if we've seen any instances of his doing anything that would require that he actually look at something, for instance reading, noticing a person's expression, etc. I can't think of any, and in fact it seems as though he gets most of his cues from sound rather than vision.
I've got a theory about this, but first I'd like to see if those who know the series better than I do can point out anything I've missed.