dumber than a box of rocks vs not the sharpest tool in the shed

dumber than a box of rocks

adj

  • Very stupid. 

not the sharpest tool in the shed

noun

  • Lacking in intelligence; dimwitted. 

How often have the words dumber than a box of rocks and not the sharpest tool in the shed occurred in a corpus of books? (source: Google Ngram Viewer )