@jacob Digging around a bit, I lack a lot of necessary background knowledge in biology and pharmacology, but I think aspirin's anticoagulant effect happens by permanently disabling the ability of platelets to trigger mass aggregation and clotting. So, any platelet exposed to the ASA becomes worse at clotting for as long as the platelet stays in the bloodstream, long after the ASA has dissipated. Repeat dosing seems to be about controlling the % of nerfed platelets.