綿裡藏針 [绵里－针]

Jyutping min4 leoi5 cong4 zam1
Pinyin mián lǐ cáng zhēn

Definitions (CC-CEDICT)
  1. lit. a needle concealed in silk floss (idiom)
  2. fig. ruthless character behind a gentle appearance
  3. a wolf in sheep's clothing
  4. an iron fist in a velvet glove