It is a derivative of coumarin, a bitter-tasting but sweet-smelling substance made by plants that does not itself affect coagulation, but which is (classically) transformed in mouldy feeds or silages by a number of species of fungi, into active dicoumarol.

Dicoumarol does affect coagulation, and was discovered in mouldy wet sweet-clover hay, as the cause of a naturally occurring bleeding disease in cattle.

The mechanism of action of Vitamin K along with the toxicity of dicoumarol are measured with the prothrombin time (PT) blood test.

The cow had died of internal bleeding after eating moldy sweet clover; an outbreak of such deaths had begun in the 1920s during The Great Depression as farmers could not afford to waste hay that had gone bad.

[3] Link's work led to the development of the rat poison warfarin and then to the anticoagulants still in clinical use today.