For a whisky to be called bourbon, it must be aged in a charred oak barrel. It gives the spirits color and flavor and is aged from months to many years. The bourbon is emptied, but the barrel lives on.
The used barrels are shipped around the world to Europe, India, China where they are used to age other spirits. They showed a warehouse that just takes them in and re-ships by the thousands.
The episode had some influence on me. As I'm typing this, I'm sipping a we bit of 7 year old Whistle Pig bourbon.