"The finding of the present study [...] documenting right lip asymmetry in ANS [11, 12], which is generally assumed to be a corollary of the left cerebral specialization for speech execution [19]. In contrast, a left lip bias was found for AS and would appear to suggest that speech motor execution involves right hemisphere activation in this group of speakers." Excerpt of https://www.karger.com/Article/Pdf/287213 Seems like everyone has a slight lip asymmetry but it's the other side for stutterers.