Honeyed words, a sword in the belly
Describes a person who appears friendly and talks kindly, but who in reality is actually treacherous
Negative
这种人口蜜腹剑，谁知道他内心里打什么坏主意 | Zhè zhǒng rén kǒumìfùjiàn, shéi zhīdào tā nèixīn lǐ dǎ shénme huài zhǔyì
This kind of person is two-faced, so who knows what kind of evil intentions they're harboring
[Source]
那个口蜜腹剑的家伙骗了我的钱 | Nàgè kǒumìfùjiàn de jiāhuo piànle wǒ de qián
That snake in the grass cheated me of my money
[Source]
Snake in the grass
Two-faced
None
None
《资治通鉴》(Zī Zhì Tōng Jiàn), a vast chronological general history written by Sòng-era (宋, 960 - 1279) politician and historian 司马光 (Sī Mǎ Guāng)
The seventh emperor of the Táng Dynasty (唐, 618 - 907) had a prime minister named 李林甫 (Lǐ Lín Fǔ). 李林甫 was a crafty person of vile character, and he used despicable methods to gain and maintain his power. At one point, he used unscrupulous tactics to curry the favor of the emperor's concubine, who in turn spoke highly of him to the emperor. This ensured that the emperor trusted 李林甫 implicitly and allowed 李林甫 to maintain his position of power.
In addition to this, 李林甫 made it a point to make other ministers look bad in front of the emperor. The sneaky part was that on the surface, he acted very kindly and spoke warmly to those ministers, but then spoke poorly of them behind their backs. For example, one time he wanted to halt the political ascent of the official 李适之 (Lǐ Shì Zhī), so he went to 李适之 and told him, "There's a lot of gold within the depths of the mountain of Huá Shān (华山). If it could be mined, the emperor would be very pleased." When 李适之 heard these words, he immediately went to the emperor to request that he be allowed to start mining. When the emperor then asked 李林甫 his opinion, he replied, "I've known about the gold for ages! Unfortunately, Your Majesty's 'auspicious aura' is concentrated in Huá Shān. It would be harmful to you if anyone were to mine there, so 李适之 must have sinister intentions."
Upon hearing this, the emperor grew suspicious of 李适之 and placed little trust in him.