dumb as a sack of hammers vs retarded

dumb as a sack of hammers

retarded

adj
  • Delayed; delayed in development, hindered; impeded. 

  • Designating a parameter of an electromagnetic field which is adjusted to account for the finite speed of radiation. 

  • Extremely stupid. 

How often have the words dumb as a sack of hammers and retarded occurred in a corpus of books? (source: Google Ngram Viewer )