Good observation. This is true for most stutterers I have meet. It surprise me that we don´t discuss this enough. ¿How can we have a neurological damage or a gene that only appears on the presence of others? ¿Why we don´t stutter or surely stutter less when we: sing, whisper, talk alone, read alone, talk on unisome, talk without listen to ourself? This type of question and a keen eye is key to improving oneself.