I'm impressed with the variety of reactions that animals show. I have this to contribute.

One day, years ago, we had a number of friends over with their instruments. I remember guitar, banjo, and recorder. Maybe a mandoline. At the time, I was taking care of a friend's two cats as well as my own. After we had been playing an hour or more, a guest called our attention to the cats - they had spaced themselves on chairs, 120 degrees apart and were listening to the music with their paws tucked under their chests.

However, when my cat was staying at a friend's house one weekend, she objected seriously to the playing of Beethoven's Appasionata. (sp) It must have been too loud, because she would run and bounce on the hardwood floor, stiff-legged, so as to make as much noise as possible. People who don't know cats say things like "If she doesn't like it, she can leave" but such people don't know cats. A cat has to be in charge!