old man's pepper vs yaffle

old man's pepper

noun
  • Achillea millefolium or common yarrow, a flowering plant native to temperate regions of the Northern Hemisphere. 

yaffle

noun
  • The European green woodpecker, Picus viridis. 

verb
  • Of the green woodpecker: to make its distinctive cry. 

How often have the words old man's pepper and yaffle occurred in a corpus of books? (source: Google Ngram Viewer )