The Chinese idiom "守口如瓶" (shǒu kǒu rú píng) is formed through a vivid metaphorical structure, combining a verb-object phrase with a simile. The first two characters, "守口" (shǒu kǒu), literally mean "guard the mouth," indicating the action of controlling one's speech. This is then directly compared by the conjunction "如" (rú), meaning "like," to the final character "瓶" (píng), meaning "bottle"—a sealed vessel that prevents its contents from spilling out. Thus, the entire construct paints a concise image of maintaining strict secrecy by being as tightly closed as a stoppered bottle, a phrase historically used to advise discretion and has been attested in classical texts like the writings of the Song Dynasty.