fVIII shows distinct binding characteristics when bound to platelets activated by thrombin plus agonists (“superactivated platelets”), such as collagen or A23187 vs by thrombin alone. (A) Platelets activated in the presence of collagen or other agonists undergo shape changes, expose more PS, and bind more coagulation factors. (B) PS comprises most of the fVIII-binding surfaces on superactivated platelets (left), whereas binding to less-activated platelets generated by thrombin alone is mediated by fibrin (right).