I guess that Gracie is somewhat odd in that she only barks and gets crazy when she plays. However, her idea of playing is a fight. She grew up with a litter of kittens that I had taken in. We kept one of them and she and that cat still love to wrestle and play. Gracie will get all wound up and dance around Missy while Missy lays there and waits for Gracie to get close enough to wrap her arms around her and get her in a wrestling hold. It is hysterical to watch but it does get noisy. Gracie may also get a bit defensive and crazy if she thinks one of the cats is getting too close to one of her precious balls. That gets her really mad (if she is not napping) and a cat may very well get bonked with the ball when Gracie tells them they have gotten out of bounds.
When someone comes to the door Gracie will do a little whiney noise because she is so excited to have someone visit her. Yes, everyone who comes to the door is there to visit Gracie....at least in her mind.
We did recently discover one other thing that sets Gracie off. We had a black bear visiting the bird feeder outside my bedroom window at night for a few weeks this spring. Every time that bear would be out there Gracie some how knew and would growl and bark like crazy if it was 9:30 at night or 3am. She may not be a good guard dog against humans but if a bear ever comes to the door I think I'm safe.