flexible vs stiff as a board

flexible

noun
  • Something that is flexible. 

adj
  • Capable or being adapted or molded in some way. 

  • Capable of being flexed or bent without breaking; able to be turned or twisted without breaking. 

  • Willing or prone to give way to the influence of others; not invincibly rigid or obstinate. 

stiff as a board

adj
  • Very stiff. 

How often have the words flexible and stiff as a board occurred in a corpus of books? (source: Google Ngram Viewer )