The first people to discover Warfarin were farmers in Wisconsin. They were confused why their cows were dying even without any obvious injuries. They eventually found out that something in the spoiled sweet clover hay leaf was killing them. A farmer took the leaf and his dead cow to a scientist, Karl Paul Link in 1933. Seven years later, Link successfully strained out the medicine Dicumoral, a strain of Coumadin which is still used today in surgeries. Link also knew that Warfarin could be used as a rodenticide by making rats essentially bleed out over a long period of time. Since then, some rat populations have built up a tolerance for Warfarin but more effective rodenticides have been created in result to this immunity. Interesting Fact: The substance is called Warfarin because Link turned over his patent for Warfarin to the Wisconsin Alumni Research Foundation or WARF hence WARFarin.