So I'm reading this book, Lost Country Life, about agricultural methods in medieval England. One of the things the author keeps doing is noting elements of those methods that remain in the language. For example, "by hook or by crook," but not by saw or axe, regulates how shepherds are allowed to take wood from a tree. They can knock down dead wood, but can't cut live branches, using only their hooks and their crooks in the process.
"Earmarks" are notches and holes in the ear of a sheep that document its ownership and breeding history.