Does Appearance Really Matter?
We learn in a beraita, “If human blood is on a loaf of bread, it needs to be scraped away before the bread may be eaten; if blood is between one’s teeth, however, one may just swallow it without concern.”
Although the Torah prohibited consumption of animal blood, it did not ban human blood. Nevertheless, we see in this beraita that there is an issue with consumption of human blood.
According to the Rambam our Sages decreed that human blood that separated from the body — such as bleeding from a cut or spit from the mouth after flossing — has the status of forbidden food, just like any other item that is prohibited according to Rabbinical Law.
However, according to the Tur and the Shulchan Aruch there is no “absolute” Rabbinical prohibition against consuming human blood. Rather, there is an issue in play known as marit ayin, that might lead to forbidding consumption of human blood under certain circumstances. “Marit ayin” translates as “appearance to the eye,” which means that a person might see something that is actually permitted, but mistakenly think that it is actually something else, which could lead the person to transgress. For example, take the case of a person hanging clothing on Shabbat that became wet from rain on Shabbat or was laundered but not dried before Shabbat. One who sees the person hanging the clothes to dry might think that the person washed them on Shabbat — and mistakenly conclude that washing on Shabbat is permitted. Therefore, hanging wet clothing on Shabbat is forbidden due to the principle of marit ayin.
There are two major practical differences that need to be noted when discussing whether something is forbidden because it is a truly prohibited item or whether it is forbidden because of marit ayin.
One difference: If it is forbidden due to marit ayin, then if it is obviously a permitted item there would be no problem. For example, the gemara teaches the example of fish blood in a bowl that also contains fish scales. Since it is self-evident that the blood is from fish and not from a forbidden source, there is no prohibition. Another halachic example is the need to put almond slices into almond milk when drinking it with meat to show that it is not dairy milk. Perhaps the modern equivalent of this case is leaving the pareve milk carton on the table when using a non-dairy coffee-creamer with a meat meal.
However, an item that is outright forbidden (such as human blood according to the Rambam) retains a forbidden status despite any “cosmetic” attempts to make it look okay.
A second practical difference that is important to note is the factor of “place.” Where is the item being consumed or the action being performed? If the problem is one of marit ayin, then there is an argument to be made that the problem exists only when in public since the rationale for this issue is that one might see it and get the wrong idea. However, if the problem is that there is a clear prohibition involved, then the prohibition should exist even in private. Accordingly, permitting swallowing blood inside the mouth is easier to understand according to the reason of marit ayin. If human blood is a clear item of prohibition, however, the commentaries explain that the Rabbis did not declare a prohibited status on human blood if it never left the body. (See Aruch Hashulchan Yoreh Deah 66:35, who writes about this second practical difference, and discusses at length how this would apply in light of the well-known teaching in Shas that “anything forbidden because of marit ayin is forbidden even in one’s innermost room.”)
- Keritot 22a