Well I be doggone... that's something I did not know. There was a story of a lost child some time back who had his dog to keep him warm as the temp plummeted, and likely kept him alive. Many of the other expressions are fairly intuitive.
"Three dog night.."
Way back farther thatn I care to admit, teenagers, going to concerts and other attractions, would brag when the police brought out canine patrols.
A "three dog night" was a pretty good time.