The blood oath seems to be a common trope in fiction. Both participants would put their own blood on the line for a pact or agreement. However, does this hold much truth? Were there any famous, verifiable instances of a blood pact like this?
From the part of history that I study (ancient Chinese history up to Jin dynasty), I cannot find any instances of blood oaths where a person's own blood is used. However, blood oaths were often conducted with the use of animals blood (chicken, dog or occasionally horse), where the blood is smeared on the lips or mixed into wine that is drunk while the oath is sworn. [source: Records of the Grand Historian, chapter on Yu Qing 虞卿]