Ben Sira 19:27

27 Casting down his countenance, and making as if he heard not: where he is not known, he will do thee a mischief before thou be aware.

Ben Sira 19:27 In-Context

25 There is an exquisite subtilty, and the same is unjust; and there is one that turneth aside to make judgment appear; and there is a wise man that justifieth in judgment.
26 There is a wicked man that hangeth down his head sadly; but inwardly he is full of deceit,
27 Casting down his countenance, and making as if he heard not: where he is not known, he will do thee a mischief before thou be aware.
28 And if for want of power he be hindered from sinning, yet when he findeth opportunity he will do evil.
29 A man may be known by his look, and one that hath understanding by his countenance, when thou meetest him.
The King James Version is in the public domain.