Neurophysiologically, there is a significant difference between "talking" and "communicating". Both talking and communicating require motor planning and speech coordination. Communicating requires a host of other processing resources. Your communication partner(s) are sending lots of verbal, visual, and social-emotional input that needs to be processed in real-time and simultaneously incorporated into your own response. Many people have an easier time talking to babies and animals, and it's because they produce less input to be processed ("input" includes anything from linguistic content to social judgments). This might be why some people don't stutter when acting. Performing a scene with a predetermined script and totally predictable set of responses means more neurological resources for other functions.