drop in the sea vs mustard seed

drop in the sea

noun
  • A very small or insignificant amount; something of little importance. 

mustard seed

noun
  • A small amount. 

  • Small lead shot, usually of size No. 12, used for shooting birds and other animals at close range. 

  • A small, round seed of the mustard plant. 

How often have the words drop in the sea and mustard seed occurred in a corpus of books? (source: Google Ngram Viewer )