The mouth, the fourth of the five officers, carries the name Gatekeeper Officer, chu na guan, the officer of output and intake, a title built around a simple physical fact the tradition treats as interpretively significant rather than incidental: the mouth is the single gate through which both food and words pass, the body's intake of sustenance and its output of speech sharing one physical opening. Reading the mouth for shape, colour and proportion, looking for lips neither too thin nor too full, evenly matched top and bottom with a well defined bow, the system draws on that double function to justify reading the feature for both material fortune, since intake governs sustenance and by extension prosperity, and for trustworthiness, since output governs the words a person keeps or breaks.
Well proportioned, evenly coloured lips are read as a sign of trustworthiness and good fortune in later life, while a crooked, badly matched or pale mouth is read as a caution about broken promises or poor fortune in old age, a pairing of moral and material readings at the same feature that echoes the mouth's own double physical role as gate for both.
The mouth's placement also ties it directly to the Lower Court, the third of the three courts, since chu na guan sits entirely within the stretch of face the courts read as governing life from roughly fifty onward. A reading of trustworthiness and fortune late in life at the mouth therefore sits inside a second, coarser claim the Lower Court already makes about the same years, one more point in the system where a five officer reading and a three court reading converge on the same feature rather than working in isolation from each other.