flexion vs writhe

flexion

noun
  • The state of being bent or flexed. 

  • Deviation from straightness. 

  • The act of bending a joint, especially a bone joint; the counteraction of extension. 

writhe

noun
  • A contortion. 

  • The number of negative crossings subtracted from the number of positive crossings in a knot 

verb
  • To twist bodily; to contort one's self; to be distorted. 

  • To twist, wring (something). 

  • To extort. 

  • To contort (a part of the body). 

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