in heat vs rock hard

in heat

prep
  • in estrus; receptive to mating 

rock hard

adj
  • With strongly held beliefs and opinions, deep conviction. 

  • As tough, hard, or inflexible as a piece of rock. 

  • With muscles developed and toned to a high degree, especially the muscles of the abdomen. 

  • Having a very fully erect and stiff penis 

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