Anxiety can make stuttering worse, but that's not the main cause. I remember reading in a textbook for speech pathologists that stuttering only happens with bi-directional communication. So I (and others who stutter) can talk to myself, or animals, or even sing - but talking to *people* is the issue. I don't remember the exact neurological mechanism that causes this, but it's helpful to know this is common with just about everybody who stutters.