sift vs thresh out

sift

verb
  • To separate or scatter (things) as if by sieving. 

  • To sieve or strain (something). 

  • [+object] (archaic or old-fashioned) To scrutinise (someone or something) carefully so as to find the truth. 

  • [+ through (object)] To carefully go through a set of objects, or a collection of information, in order to find something. 

thresh out

verb
  • To extract or remove by threshing. 

  • To thrash out. 

How often have the words sift and thresh out occurred in a corpus of books? (source: Google Ngram Viewer )