LUCASTA, frown, and let me die, 
  But smile, and see, I live; 
The sad indifference of your eye 
  Both kills and doth reprieve. 
You hide our fate within its screen; 
  We feel our judgment, ere we hear. 
So in one picture I have seen 
  An angel here, the devil there.
Richard Lovelace
http://www.poemhunter.com/poem/to-lucasta-her-reserved-looks/