Avodah Zarah, Chapter One, Mishnah Five
This mishnah begins a somewhat new topic: things which are forbidden to sell to idolaters at all times of the year and not just during their holidays, lest these things be used in idol worship. Again, it is not only forbidden to worship idols, but it is forbidden to aid non-Jews in idolatry.
1) The following things are forbidden to be sold to idolaters: iztroblin, bnoth-shuah with their stems, frankincense, and a white rooster.
2) Rabbi Judah says: it is permitted to sell a white rooster to an idolater among other roosters; but if it be by itself, one should clip its spur and then sell it to him, because a defective [animal] is not sacrificed to an idol.
a) As for other things, if they are not specified their sale is permitted, but if specified it is forbidden.
3) Rabbi Meir says: also a good-palm, hazab and niklivas are forbidden to be sold to idolaters.
Section one: Iztroblin are the pines of a cedar tree. Bnoth-shuah are types of figs. All of these things listed in this section are used by the idolaters for idol worship. Therefore it is forbidden to sell them to non-Jews since that would be abetting idolatry.
Section two: Rabbi Judah presents some exceptions to the prohibition of selling a white rooster to an idolater. A Jew may sell a white rooster to an idolater if it is sold with other regular roosters. In this case the Jew is merely selling roosters and happens to sell one that is white. The non-Jew may also not be purchasing the rooster for idolatrous purposes since he bought a lot of other roosters. Furthermore, when he sells the white rooster it doesnt look to others as if he is selling something specifically for idol worship, since the other roosters he is selling will not typically be used in idol worship. Rabbi Judah also creates a way for Jews to sell white roosters alone to idolaters. As long as the Jew cuts off the spur the sale is permitted since the idolater will not sacrifice a blemished animal.
With regards to the other forbidden items, it is forbidden to sell them to idolaters only if the sale is specifically for idol worship. If not, it is permitted to sell the item, because it may be used for other, non-idolatrous purposes.
Section three: Rabbi Meir adds several other things which are forbidden for a Jew to sell to idolaters. All three of these are varieties of date-palms.