Avodah Zarah, Chapter Two, Mishnah Three
This mishnah lists things that belong to non-Jews that may not be used by Jews, for fear that the Jew will be using something that has previously been used in idol worship.
1) The following things belonging to non-Jews are forbidden [for Jews to use] and the prohibition extends to any benefit that may be derived from them:
ii) or a non-Jews vinegar that was formerly wine,
iii) Hadrianic earthenware,
iv) skins pierced at the animals heart.
(1) Rabban Shimon Gamaliel says: when its tear is round, [the skin] is forbidden, but if oblong it is permitted.
2) Meat which is being brought into a place of idol worship is permitted, but that which is brought out is forbidden, because it is like a sacrifice to the dead, this is the opinion of Rabbi Akiba.
3) With non-Jews going on a pilgrimage [to worship idols] it is forbidden to have any business transactions, but with those returning it is permitted.
Section one: Non-Jewish wine may not be used since it may have been used in making a libation to an idol. [This prohibition is still observed by many religious Jews today, even though we can be quite sure that the wine was not used for idol worship.] Similarly, vinegar that was once intended to be wine and then went sour may not be used by a Jew, since it may have been used in idol worship when it was wine. However, if the non-Jew bought the vinegar from a Jew and then gave it back to a Jew the Jew may use it since vinegar itself is not used in idol worship.
According to the Talmud Hadrianic earthenware absorbs wine and when subsequently wetted, will release the wine. If a Jew were to use such earthenware he would be using non-Jewish wine, which is prohibited.
According to the mishnah, idolaters would make incisions in animals to remove the hearts and use them in idol worship. If one sees a cut in an animal skin at the place of the heart, it is a sign that the animal was used for idol worship and it is forbidden. Rabban Shimon ben Gamaliel claims that only if the cut is circular is the skin forbidden. Since non-Jews do not make oblong cuts as part of their idol worship, the skin is permitted.
Section two: Meat that is being brought into a place of idol worship is permitted to a Jew, since it has not yet been used for idol worship. It is of course not permitted to be eaten, since it probably is not kosher. However, one could use it to feed animals. Meat that is coming out of a place of idol worship is forbidden, since it was probably used for idolatry.
Section three: It is forbidden to conduct business with non-Jews who are on their way to worship idols, since they will thank their gods for their business with the Jews. In this way the Jew will indirectly be abetting idol worship. However, it is permitted to engage them in business on their return, since they have already completed their idol worship. [Note this last section is of a different subject than the other sections. It should have been included in chapter one. It probably was included here due to its similarity to the previous clause.]