Chullin 41: Where Blood May Flow, the Appearance of Appropriateness

We are introduced to a new Mishna that teaches more about sacrifice and blood and what is permitted.  It teaches that the blood of a slaughter cannot flow into the sea, the rivers, or a vessel, because that has the appearance of idolatry.  If the blood flows into a round excavation containing water, it is permitted.  Similarly one may slaughter an animal while on a ship into a vessel because it is obvious that one is attempting to protect the ship.  One is not permitted to have animal's blood flow into a small hole in the ground, but it is permitted to have the blood flow into a small hole within one's home.  In the marketplace this is not permitted, again because it has the appearance of idolatry.

The rabbis go on to discuss the differences between sacrifice inside and outside of the Temple.  The Gemara demonstrates the many different opinions that prevail regarding what is permitted and what is not permitted. 

Mayin ha'ayin, the perception of  what an action might engender in others, is a prominent concept.  In today's society, this reminds me of the legal concept "the appearance of justice".  One reason for this rule is that others might believe that something is permitted when in fact it is not.  In addition, this is a justification for stringency in rulings.