Is it when you are talking out loud or even when you are whispering, sometimes I might struggle with a word that is not familiar and when I talk out loud to myself it’s sorta like I’m talking to people and might have a slight block on certain sounds but overall it’s a mystery. I think it has to do with being forced to think or and that can slow down our speech which can lead to stuttering moments but I would assume for most of us, the stuttering moments/ blocks we have when we are alone is much less intense and no emotions are attached to it, at most we are surprised on how it’s possible but we aren’t feeling anxious about it