To hide a dagger in a smile; to conceal evil intentions behind a facade of friendliness; honey-mouthed and dagger-hearted.
他总是对别人笑脸相迎，却不知道他内心深处蜜里藏刀，随时可能给人使绊子。
He always greeted people with a smile, unaware that deep down he was honey-mouthed and dagger-hearted, ready to trip someone up at any moment.
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