facial expression vs mien

facial expression

noun
  • The expression or countenance that seems to an onlooker to be represented by the appearance of a person or animals's face, resulting from specific use of that person's facial muscles. 

mien

noun
  • A specific facial expression. 

  • Demeanor; facial expression or attitude, especially one which is intended by its bearer. 

How often have the words facial expression and mien occurred in a corpus of books? (source: Google Ngram Viewer )