Red River ox carts were a vital form of transportation during the 19th-century westward expansion in the US and Canada. They carried fur to trading posts in places like St. Paul, Minnesota, and then carried supplies back to settlements along the Red River of the North, which now forms the Minnesota–North Dakota border. Built entirely of wood and animal hide—and no metal—the carts typically had two wheels, which were notorious for their constant creaking. Why couldn’t their axles be greased? Discuss