Right at the end of the vid, you can hear the "noisy breathing". Behaviorists are of the mind that the audible breathing is akin to primate laughter or joy. Pay attention to when Zeus is being quiet vs. the audible breathing, I think they might be on to something. I never paid it any attention until I read about it, but thinking back I think I knew it subconsciously I would relax when I heard him breathing loudly and worry when he was quiet..
Never cook bacon while naked.