Your definition of the internal hush seems to involve choosing when and where and how to say something. I'd simply call that wisdom and discretion. What do you have to say about self-censorship? How is that different from shyness? All these ideas are building towards something poetic.
Yes, but for me that often ends up in a hush and self-censorship. There are many thoughts and feelings I have that are not shared because I censor myself a lot. What I say, and what I don't say usually have a rational behind it and I'm not exactly known to be a very open person. It's a difference from shyness, which I think can stem from anxiety or worrying about peoples reaction to what you are saying. For me, it's more calculated, more planned out, and a function of at times obscuring what I feel and what I want people to think.