Somewhat agree here. It is a display. How meaningful I really do not know. I had an older fellow tell me once it was a sign the dog was turning on, really wanting it for himself. Sort of like naturally starting vs. having 'starting' thrust upon the dog.
I have seen it in both game dogs and in cur dogs but one thing both have in common is intensity. The dogs that have the knot/raised hair on the tale are usually more intense. EWO