In a century of study, no one has managed to make these knots talk. But recent breakthroughs have begun to unpick this tangled mystery of the Andes, revealing the first signs of phonetic symbolism within the strands. Now two anthropologists are closing in on the Inca equivalent of the Rosetta stone. That could finally crack the code and transform our understanding of a civilisation whose history has so far been told only through the eyes of the Europeans who sought to eviscerate it.