I think maybe y'all're lookin' a mite too hard. The only times I ever see this cartoon is when it's referred to here, so I don't know whether the dog is normally deeply insightful, or what. But through a stranger's eyes (mine), I would say that the toga and the Latin (which even I was able to connect to ululate) are because of the ref. to the ancient Romans. And now, to get to the crux of the matter, I would say that the facial expression plus the use of the period (indicating no particular emotion), together serve to demonstrate the dog's utter lack of interest in the stated "facts". Like I have used woo, as in: "My big excitement of the day was that I went to the grocery. Woo."
Sometimes it is the simple answer.