A knife in the mouth and a bean in the heart means that a person is cruel in the mouth and kind in the heart, but his way of speaking is not easy to accept, but it is not harmful.

Hiding the knife in the smile is the opposite.

Refers to a hypocritical and vicious villain. Treat people with kindness on the surface, but they are insidious and cunning.

I'd rather have a knife in my mouth than a knife hidden in my smile. That's kindness from my heart.

Even if you don't speak correctly, don't be a sinister villain.