Something to ponder. This metaphor, which implies that the mind can chew or digest an idea, dates from the early nineteenth century, although words to that effect were cited by Erasmus in his Adagia of the sixteenth century (“Nor try to put courteous conversation into the minds of impudent men, for speech is the food of thought”). The modern cliché was used by Mark Twain (A Connecticut Yankee in King Arthur’s Court, 1889): “There was food for thought there.”