keel over vs knock over

keel over

verb
  • Of a vessel: to roll so far on its side that it cannot recover; to capsize or turn turtle. 

  • To collapse in a faint; to black out, to swoon. 

  • To die. 

knock over

verb
  • To bump or strike something in such a way as to tip it 

  • To rob; to stage a heist of. 

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