Nature summarizes a study by Anna Taylor, who examined the specific features of a dog’s growl that humans use to estimate the dog’s size. As it turns out, we rely on pitch in a dog’s growl in the same way that we use pitch to estimate size in our fellow humans. A novel area of focus in the burgeoning interest in researching communication between humans and dogs!
http://www.nature.com/news/2008/080523/full/news.2008.852.html