That's interesting! My dogs all bark in different situations: Pup barks all the time outside, like she is our watchdog; Buddy barks at squirrels and strange noises; Boo barks when she is startled/spooked; and Paula only barks when she wants to play with Buddy. The last one is intriguing to me - I used to think that she was being mean to him, picking on him, but after observing the way Paula bounces and barks and nips at Buddy, I've concluded that she is simply trying to instigate him to play with her. I guess Paula has the 'harmonic bark' but not the 'noisy bark!'