Researchers at the Max Planck Institute of Colloids and Interfaces and collaborators at the University of California at Santa Barbara and the University of Chicago believe they have uncovered the basis how marine mussels use the byssus, a bundle of tough and extensible fibres, to fasten securely to wave-swept rocky coastlines. According to their findings, local accumulation of iron-mediated cross-links creates hard knobs within an extensible matrix containing much fewer of these molecular bridges.