Avodah Zarah 35 - Real Reason for Prohibiting Cheese of Idol Worshippers
If one betroths a woman using the waste of an ox that is stoned - for example, because it was sodomized - the betrothal is valid, but if he uses the waste of calves sacrificed for idolatry, the betrothal is invalid. Why? Regarding calves sacrificed for idolatry, the fatter it is the better, and the owner is pleased with the waste expanding its size. With an ox that was stoned, the owner does not care if it is fat or not, and the waste is not part of it.
This law has direct connection to the cheese prohibition : rennet, being a separate milky substance in the stomach of a ruminant, should not make the cheese prohibited. When Rabbi Yehoshua avoided saying the reason why the cheese of idolaters is prohibited , he did so because a year had not yet passed since the decree was promulgated, and he did not want people to argue about its reasons. That is why he hinted to a kiss that seals the lips . The two most prominent reasons are the snake venom in the milk and using the actual meat part of an animal (maw). Tosafot say that now the snakes are not prevalent and the cheese is permitted, but Rashi and others disagree.
Art: Edwin Lord Weeks - The Snake Charmers Bombay