the milk of human kindness
US /ðə mɪlk əv ˈhjuː.mən ˈkaɪnd.nəs/
UK /ðə mɪlk əv ˈhjuː.mən ˈkaɪnd.nəs/

1.
natural human sympathy, compassion, and benevolence
:
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Despite his tough exterior, he still had the milk of human kindness within him.
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Her cruel actions showed a complete lack of the milk of human kindness.