The Inca never developed a system of writing, but they kept records and told stories through intricate knotwork. Learn what researchers know -- and what they're still looking to find out -- about Inca khipu in this classic episode of BrainStuff, based on this article: https://people.howstuffworks.com/culture-traditions/cultural-traditions/unraveling-khipu-inca-knot-language.htm