How do blood clots maintain that precise balance of stiffness for wound healing and flexibility to go with the flow? Researchers at the University of Pennsylvania School of Medicine and the School of Arts and Sciences have shown that a well-known protein structure acts as a molecular spring, explaining one way that clots may stretch and bend under such physical stresses as blood flow. They report their findings in a Letter in the latest online edition of the Biophysical Journal. This knowledge will inform researchers about clot physiology in such conditions as wound healing, stroke, and cardiovascular disease.