Different people have different views about blocks. Some people view them as an avoidance behavior, not one we do consciously, but one that we have become conditioned to do. We are trying to avoid stuttering, because we are trying to say what we want fluently, but it won't come out fluently. So, in order to get out of a block...you have to get into a stutter! Get on the sound you want to say. It will probably be stuttered on, but at least this moment of stuttering will be forward moving, not a total blockage of air. Stay on the sound or in the stutter as long as you need to, until you can easily release the stutter or sound and say the rest of the word. Stutter on it how your body wants to stutter on it! Sit in the stutter, don't try to force yourself out of it. Trying desperately to get out of a moment of stuttering creates tension, including the contorted face you are mentioning. By expecting your are going to stutter and allowing yourself to stutter, lots of the tension melts away. Of course it takes a while to shift your mindset from "avoiding stuttering at all costs" to "allowing yourself to stutter." But, man, what a happier and easier way to live!