As for how long it takes to pass black stools after eating pig’s blood, the reason for passing black stools after eating pig’s blood is that after eating pig’s blood, the blood contains more iron, which is decomposed and oxidized by gastric acid after entering into the human body, and then there is a reaction of synthesis between the iron and gastric acid, which results in the formation of black stools, and so the stools will be black. Such black stools can usually be eliminated 1-2 days after eating pig’s blood. If the stools are still black after 2 days, high attention should be paid to see if there is gastrointestinal bleeding. If there is still black stool after 2 days, and the patient is accompanied by darkness, dizziness, panic, etc., it is recommended that the patient go to the hospital for a stool test to look at the fecal occult blood, blood routine, hemoglobin, to see if there is anemia, whether there is gastrointestinal bleeding, and if necessary, it is recommended that the patient undergo a gastroscopy examination.