I was learning Mishna (Chulin 2:9) with my son and we came across the following passage which also appears in the Tosefta (Chulin 2:6):
אין שוחטין לא לתוך ימים ולא לתוך נהרות ולא לתוך מים עכורין אבל שוחט או לתוך אגן של מים ובספינה על גבי כלים ואם אין לו מקום מקום בספינה שוחט לתוך הים ואם אין רוצה לטנף את ביתו שוחט לתוך כלי או לתוך גומא ובשוק לא יעשה כן מפני שעושה את חוקי מינין אם עשה כן צריך בדיקה. הבשר שנמצא ביד גוי מותר בהנאה ביד המין אסור בהנאה.
We do not slaughter [animals for food, so that their blood spills directly] into seas, and not into rivers, and not into standing water. But he [can] slaughter [such that the blood spills directly] either into a water hole, or [if he is] on a ship [then] on top of vessels. But if he does not have [enough] room on the ship [he can] slaughter [so that the blood spills directly] into the sea. And if he does not want to make his house dirty [he can] slaughter [so that the blood spills directly] into [an empty] vessel or into a hole [made in the floor of the house]. But in the market place he should not do this, because [this is considered to be] doing an act of sectarians (Minim). [But] if he [already] did this [then] he needs to be checked [out by the Bet Din if he is really a sectarian and therefore should be kicked out from the Jewish community or not]. Meat that is found in the hand of a Non-Jew is permitted to be benefited from, but [meat that is found] in the hand of a sectarian (Min) is forbidden to be benefited from.
The reason why animals cannot be slaughtered so that their blood spills in all of these things is because onlookers might say that the person is not slaughtering this animal for food, but is rather sacrificing it to the god of that object. For example, it was a common practice among Greeks and Romans to slaughter animals directly over the water of the sea while traveling on a boat in order to appease the god Poseidon (god of the sea) so that he would not bring a storm and wreck the ship. What caught my attention was the last statement of the Mishna and the Tosefta which says that in the market place a person cannot slaughter an animal into a vessel or a hole in the ground, because that would be acting like the law of the sectarians (Minim), and therefore onlookers might suspect him to be one of these Minim. From the following statement in the Tosefta it is obvious that Minim are not regular Non-Jewish idol worshipers, because it says that it is permitted to receive benefit from a piece of meat found in the hand of a Non-Jew, but not permitted if it is found in the hand of a Min. So who are these Minim and what did they actually do in public places that would cause the Rabbis to prevent the Jews from doing it so that they would not be suspected to be Minim and if they were seen to do so then they had to be investigated by the Bet Din as a suspect Min?
The Hebrew word Min (literally: type) usually refers to some kind of sect of Jews who have deviated from normative Rabbinic Judaism and created a sort of their own religion. As a generalization the Rabbis have viewed Tzedukim (Sadducees), early Jewish Christians (Notzrim or Nazarenes as they called them), and Essenes as sectarian Jews and applied the word Min to them as a general term. However in this particular case it would be a major oversimplification and would not do them justice to apply this term generically, because it is obvious that the Mishna and the Tosefta are referring to a very particular practice of a particular sect, which made was a clear sign of membership that made the Rabbis very nervous. Here Min cannot refer to a regular Jew who decided to worship idols as some commentators have suggested, because an idol worshipping Jew would simply be called a Yisrael Mumar (A Jewish Transgressor) and they would not need to make a whole investigation in court to find out who he really is, because such a Jew did not pose any danger to the community. He was simply violating a Torah law and had to be punished for his actions, but nothing more than that.
I was not able to figure out which specific sect the Mishna and the Tosefta refer to. Anyone who can shed light on this issue please post in comments or write to me at firstname.lastname@example.org.