confound vs throw a spanner in the works

confound

verb
  • To perplex or puzzle. 

  • To combine in a confused fashion; to mingle so as to make the parts indistinguishable. 

  • To stun or amaze. 

  • To make something worse. 

  • To cause to be ashamed; to abash. 

  • To defeat, to frustrate, to thwart. 

  • To fail to see the difference; to mix up; to confuse right and wrong. 

noun
  • A confounding variable. 

throw a spanner in the works

verb
  • To introduce a problem, dilemma or obstacle, something unexpected or troublesome. 

How often have the words confound and throw a spanner in the works occurred in a corpus of books? (source: Google Ngram Viewer )