dog vs swine

via vintageimages.com

Since I found this curious scene at vintageimages.com I haven't got its backstory, but I think it's a blind man's trained dog showing off his sign to a pig.  I liked the quality of the work, but puzzling over the action is what won my heart.  Was the dog able to communicate with the pig in the original story?  Or was he simply a trained and loyal helpmeet who knew only how to sit up and show his sign whenever he could?