Speech muscles are very coordinated and flow loosely as we speak. When we stutter or stammer we are over-tensing these muscles which restrict and stop air flow. There is no words if air isn’t flowing over our vocal cords. Sometimes it’s best to be open about and instead of trying to hide it (tenses up) just be open about your stutter/block and the words will start to come more natural. Have you ever tried to stutter? Sounds easy doesn’t it? Give it a shot in front of someone :)