綿裡藏針

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

Character by character

• 綿(mián)silk floss
• 裡(lǐ)lining
• 藏(cáng)conceal
• 針(zhēn)needle