Honeyed Lips, Sworded Heart: This idiom is used to describe someone who speaks sweetly and pleasantly, like honey, but secretly harbors malicious intentions to harm others.
The idiom originates from the "Zizhi Tongjian (Comprehensive Mirror to Aid in Government), Tang Dynasty Annals, the First Year of Emperor Xuanzong's Tianbao Reign": "When Li Linfu served as chancellor... he especially resented men of letters and talent. Sometimes he would pretend to be friendly with them, luring them with sweet words while secretly plotting their downfall. People of the time said of Li Linfu, 'He has honey on his lips and a sword in his belly.'"
Li Linfu held the positions of "Minister of War" and concurrently "Zhongshu Ling" during the reign of Emperor Xuanzong of Tang, which amounted to being a chancellor. In terms of artistic talent, Li Linfu was actually quite accomplished—he could write and paint well. However, in terms of moral character, he was utterly despicable. He was envious of talent and sought to harm others. Anyone who surpassed him in ability, reputation, or who held a position of power and status comparable to his own, he would use every underhanded method possible to suppress and eliminate. Towards Emperor Xuanzong, he possessed a special skill in flattery and obsequiousness. He made every effort to accommodate the emperor and employed various tactics to curry favor with the emperor's favored consorts and trusted eunuchs, securing their goodwill and support to protect his own position. When Li Linfu interacted with others, he always appeared outwardly kind and approachable, uttering nothing but pleasant and seemingly well-meaning words. In reality, however, his character was extremely treacherous and cunning, frequently scheming to harm others behind the scenes. For example, on one occasion, pretending sincerity, he said to his colleague Li Shizhi: "Mount Hua is rich in gold. If we could mine it, the nation's wealth would increase greatly. It's a pity the emperor doesn't know about it."
Li Shizhi took this at face value and quickly rushed to advise Emperor Xuanzong to begin mining operations. The emperor was delighted upon hearing this and immediately summoned Li Linfu to discuss the matter. Li Linfu, however, replied: "I've known about this for a long time. Mount Hua is a place where the imperial family's 'feng shui' converges—how could we casually mine it? Those who urge you to mine it probably have ill intentions. I've wanted several times to tell you about this, but I've been too afraid to speak up." The emperor was deeply moved by these words, believing Li Linfu to be a truly loyal and patriotic minister, while becoming very displeased with Li Shizhi and gradually distancing himself from him.
Thus, relying on this special "skill," Li Linfu remained chancellor for more than a decade.
Later, when Sima Guang of the Song Dynasty compiled the "Zizhi Tongjian," he evaluated Li Linfu, pointing out that he was a man with "honeyed lips and a sworded heart"—a description that was very accurate.