cook up vs knock together

cook up

verb
  • To manufacture; to invent (something, often a deceit or falsehood). 

  • To manufacture a significant amount of illegal drugs (LSD, meth, etc.) 

  • To prepare a heroin dose by heating. 

  • To prepare (food or chemical substances) by cooking or heating. 

  • Used other than figuratively or idiomatically: see cook, up. 

knock together

verb
  • To assemble something quickly; to knock up. 

How often have the words cook up and knock together occurred in a corpus of books? (source: Google Ngram Viewer )