Sharp as a dagger
Have a mouth as sharp as a dagger but a heart as soft as tofu.
~ Chinese Proverb
mouth
With mouth open
Man who stand on hill with mouth open will wait long time for roast duck to drop in.
~ Confucius
It might have been
Of all sad words of mouth or pen, the saddest are these: it might have been. ~ John Greenleaf Whittier
Open your mouth
Open your mouth only if what you are going to say is more beautiful than silence. ~ Anonymous