colt's tooth vs libido

colt's tooth

noun
  • Youthful desires, especially lust. 

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

libido

noun
  • Sexual urges or drives. 

  • Drives or mental energies related to or based on sexual instincts but not necessarily sexual in and of themselves. 

  • Synonym of albedo in terms of a planet's, such as that of Mars, average surface spectral reflectivity. 

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