What kind of function does the longest gene in the human genome code for? The answer is a bit mundane: a very long molecular spring that provides muscle with passive elasticity. Nature adjusts the protein, called titin, for many types of muscle, e.g., skeletal or cardiac muscle, as well as for other cellular functions. The molecular spring contains hundreds of elastic elements in series like beads on a string. One type of bead is the immunoglobulin domain, which can stretch to ten times its normal length. For a long time only one of the immunoglobulin domains was structurally known, permitting only a single peek into nature's design library. Recently, a second domain became structurally known and protein crystallographers and modelers joined forces to discover how nature designs its beads along titin, as described in a recent publication.