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It is said that the tongue functions through extension and curling. The mouth functions through opening and closing. Each embodies its own yin and yang characteristics. Moreover, the mouth is the orifice of the Spleen (P) and the outer gate of the Heart (H). The *Nan Jing* (Classic of Difficult Issues), in its theory of the Seven Chong Gates, refers to the lips as the "Fei Men" (Flying Gate) and the teeth as the "Hu Men" (Household Gate). Through the movement of opening and closing, sounds emerge from the mouth, and food and drink enter through it. It serves as a crucial thoroughfare connecting the Zang-Fu organs. The methods for observing the morphology of the mouth are approximately tenfold: namely Zhang (Opening), Jin (Gritting/Closed), Cuo (Puckering), Pi (Deviation), Zhen (Trembling/Shivering), Dong (Moving/Flapping), He Luo (Chin Dropping), and Kou Nie (Teeth Gnashing). From these, one can distinguish between dryness and dampness, differentiate cold and heat, and thus discern the nature of the disease. Why is this so? "Zhang" manifests as opening without the ability to close; "Jin" manifests as closing with difficulty in opening; "Cuo" presents a shape of puckering and gathering of the upper and lower lips; "Pi" shows a state of laxity on one side and tension on the other; "Zhen" refers to shivering due to cold chills, with rapid trembling of the chin; "Dong" involves frequent opening and closing movements of the mouth; "He Luo" resembles "Zhang," but the chin fails to close; "Kou Nie" resembles "Dong," but involves gnashing rather than frequent opening. Dryness arises from the depletion of body fluids (Jin-Ye); dampness belongs to the slickness of saliva and phlegm. Therefore, "Zhang" indicates deficiency; "Jin" indicates excess; "Cuo" signifies the struggle between pathogenic factors and healthy qi, where healthy qi is declining and pathogenic factors are prevailing; "Pi" results from the traction of sinews and tendons, where tension represents healthy qi and laxity represents pathogenic factors; "Zhen" stems from deficiency of the Yangming channel; "Dong" originates from the exhaustion of Stomach Qi; "He Luo" indicates flaccidity of the muscles around the Jiache acupoint, indicating pathology in the Yangming meridian; "Kou Nie" suggests impending failure of the Kidney (K) system, with the disease extending to the meridians of the Stomach (S). These are all morphological manifestations of the mouth. However, although morphology is divided into dryness and dampness, both dryness and dampness have distinctions of deficiency and excess. Thus, while dryness generally pertains to heat and dampness to cold, the patterns differ according to interior/exterior and upper/lower locations, and the yin-yang states of the Zang-Fu organs vary. If one does not integrate the Four Diagnostic Methods (Inspection, Auscultation-Olfaction, Inquiry, Palpation) and reference the Five Orifices, one may know there is dryness but not why it exists, or know there is dampness but not its cause. Consequently, treating heat will not eliminate it, and treating cold will not resolve it; such an approach would be little short of acting contrary to reason. Regarding the five colors appearing on the lips and the detailed inquiry into tastes in the mouth, these must also be cross-referenced and verified together. Only then can understanding become clearer and application more effective. Furthermore, regarding impetigo-like sores (Jinyin Chuang), those flowing from the mouth to the limbs are treatable, whereas those flowing from the limbs into the mouth are untreatable. By analogy, this principle applies to smallpox, syphilis-like sores (Guang Chuang), and various painful ulcers and abscesses; their favorable or unfavorable progression follows similar principles.