What defines “Bathed in blood”?

@FrobonesSword of Kas. “If the sword isn’t bathed in blood within 1 minute…” What defines “bathed in blood”? Reducing to 1/2 HP? A hit? a hit would be good, or say a vial of fresh blood #WOTCstaff

— (((Mike Mearls))) (@mikemearls) January 5, 2017