colt's tooth vs urge to merge

colt's tooth

noun
  • Youthful desires, especially lust. 

  • One of a horse's first set of teeth. 

urge to merge

noun
  • A strong desire to form intense emotional connections, stereotypically associated with lesbians. 

How often have the words colt's tooth and urge to merge occurred in a corpus of books? (source: Google Ngram Viewer )