The medieval monks followed the Fathers in urging the practice of lectio divina, a way of reading the Scriptures. It involved reading a biblical text aloud, so that your voice muscles and your ears were involved, and of stopping when a word or a phrase or a sentence stuck you, and then ruminating on it as you murmur it, chewing on it, as our saying goes. Here’s a passage in which Augustine uses the metaphor.
The words of wisdom of the Lord God are excellent. They are served to you by us as if in small vessels, but while the vessels are made of clay, the bread comes from heaven. The Apostle said, “We have this treasure in earthen vessels so that it may be clear the power is God’s” (2 Cor 4:7). Now the treasure is the same thing as bread, for if they weren’t the same, another text would not say of the treasure: “A treasure to be desired is in the mouth of a wise man; but a foolish man swallows it” (Prov 21:20). We advise you, beloved, to store what you’ve heard in the stomach of your memory and then in a way to ruminate on them by turning them over and thinking about them. This is what that text means: “A treasure to be desired is in the mouth of a wise person, but a foolish man swallows it.” In brief, it says: A wise man ruminates, but a foolish man does not. How to say this clearly and in Latin? A wise man thinks about what he hears, while a foolish man forgets what he hears. And this was also why in the Law animals that ruminate were said to be clean, while those that don’t ruminate were called unclean (Lv 11:2-8), because every creature of God is clean. To God the creator, a pig is as clean as a lamb, since all of God’s creatures are “very good” (Gn 1:31), and “every creature of God is good,” the Apostle says,” and “All things are clean to the clean.” While in nature both are clean, as symbols the lamb means something clean and the pig something unclean. The lamb symbolizes the blameless wisdom of the ruminant, the pig the unclean foolishness of the one who forgets. (EnPs 141, 1; PL 37; 1833-1834)