invaginate vs pratfall

invaginate

verb
  • To turn or fold inwardly. 

  • To fold inward to create a hollow space where none had existed, as with a gastrula forming from a blastula. 

  • To fold up or enclose into a sheath-like or pouch-like structure, either naturally or as part of a surgical procedure. 

adj
  • Having one portion of a hollow organ drawn back within another portion. 

  • sheathed 

pratfall

verb
  • To fall on to the buttocks. 

noun
  • A fall onto the buttocks. 

  • A staged trip or fall, often for comedic purposes. 

  • A humiliating mistake. 

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