The term "protrusion" has been employed in literature to convey both literal and metaphorical extensions. For example, in Charlotte Perkins Gilman’s work, it describes a tangible outcrop of solid granite, suggesting a defined physical form [1][2]. John Locke uses the term in a natural philosophy context to discuss the inherent physical characteristics such as bodies and their mutual interactions [3][4]. In Jules Verne’s narrative, the term denotes a physical irregularity that impedes movement [5]. Most notably, Charles Darwin applies "protrusion" to human expression, repeatedly referring to the physical manifestation of emotion in the lips—whether as a sign of anger, sulkiness, or simply a common trait in children—as well as noting its occurrence in minute reactions like the erection of hairs due to tickling [6][7][8][9][10]. Through these varied examples, "protrusion" emerges as a versatile descriptor bridging the concrete and the expressive.