In actuality,the high-pitch sound of the harmonica hurts the dog's ears,so it reacts by howling.If you noticed,that's basically all it was doing-howling. I used to have dogs do the same thing every time a fire engine,or ambulance would go by.All you need to do is find something,like the harmonica or maybe a flute-something that emits a high pitch sound,and your dog will probably howl,or "sing"too! Have a good one!
