smile vs titter

smile

verb
  • To look cheerful and joyous; to have an appearance suited to excite joy. 

  • To have (a smile) on one's face. 

  • To express by smiling. 

  • To express amusement, pleasure, or love and kindness. 

  • To be propitious or favourable; to countenance. 

noun
  • Favour; propitious regard. 

  • A facial expression comprised by flexing the muscles of both ends of one's mouth, often showing the front teeth, without vocalisation, and in humans is a common involuntary or voluntary expression of happiness, pleasure, amusement, goodwill, or anxiety. 

titter

verb
  • To laugh or giggle in a somewhat subdued or restrained way, as from nervousness or poorly-suppressed amusement. 

noun
  • A nervous or somewhat repressed giggle. 

  • A woman's breast. 

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