Speech therapy today

Another amazing thing happened today! When we were at speech therapy, the therapist was kind of doing a sing-song thing while we were doing a puzzle. I know Michael normally gets upset when I sing and he was doing the same for her. He was screaming and carrying on but then all of a sudden he stopped and said "NO no sing!!!" I was amazed! He has never been verbally specific about something like that before. He has said "no stop it!" etc before but never specifics. I am really hoping this is the start of a major breakthrough in communication!