Yeah I know those differences are there in the brain because of evolutionary condition to being social. But I don't think it's *just* that. Some time back I tried to record myself speaking sentences for a job interview. This was just me recording by myself......and I still stuttered. I was not in front of someone when doing this. So clearly not a realtime social situation. I think it's got something to do with expectation. When you expect yourself to say something in a very short window of time. If you play video games, you might have noticed that if you voluntary try to aim for a headshot, it seems very difficult. Like your hand start moving inaccurately and the harder you try, the more inaccurate and clumsy your mouse movements become. The people who flick headshots do it without thinking much.