Karetot 21: Consumption of Whose Blood?

Perek V focuses on the prohibition against consuming blood that was mentioned at the beginning of this massechet.  In the Mishna, one is only liable for karet after consuming the blood of birds or animals that is released when the animal dies.  Sefer Vayikra (7:26) seems to forbid all types of blood, but a baraita teaches that blood found in eggs, fish blood, kosher grasshopper blood and human blood is not actually biblically forbidden.

The Gemara clarifies further.  Fish and grasshopper blood are not forbidden at all, though they are forbidden if placed in a cup for mar'it ha'ayin, they would have the appearance of forbidden blood.  If one left a fish scale in the cup, it would be clear that the blood was not of an animal and thus it would be permitted.  Once the blood has left a human body, there is a rabbinic prohibition against consuming it.  One need not be concerned about swallowing blood from bleeding gums.  However, if someone is eating and finds that one has bled on their food, the blood must be removed before continuing to eat.

Even though we know that appearances are important because of mar'it ha-ayin, Rashi teaches that a person can swallow blood in one's mouth because it cannot be witnessed.  Tosafot state that this is only the case when dealing with mar'it ha-ayin is connected with a biblical prohibition.  Human blood is not mentioned biblically and thus this concept does not apply.