When platelets are hyperactive, they can form blood clots that cause heart attacks or strokes. Antiplatelet drugs can combat such clotting, but reversing their effects requires waiting a week or more for new platelets to form, during which time patients could be at risk of uncontrolled bleeding. An easily reversible alternative to existing platelet inhibitors could be safer. To find a way to more carefully control blood clotting, Donald E. Ingber of the Wyss Institute for Biologically Inspired Engineering at Harvard University, Anne-Laure Papa of George Washington University, and coworkers have devised stripped-down platelet “decoys” that inhibit blood clots. Their activity can be quickly reversed by adding natural platelets (Sci. Transl. Med. 2019, DOI: 10.1126/scitranslmed.aau5898). The researchers made the decoys by extracting natural human platelets to remove most of their membranes and cellular contents. In the process, the natural platelets maintain their cytoskeleton and cell-surface receptors. Thanks to those changes, the decoys don’t aggregate, and they inhibit aggregation of normal platelets in culture and in animal studies. This suggests they might be an alternative to today’s anticlotting therapies. They also decrease metastasis in mice with cancer.