Avodah Zarah, chapter five, mishnah five. This mishnah continues the line of the preceding mishnayos: a Jew who has kosher wine in his possession, and a gentile who is nearby and has potential access to it. As in the earlier mishnayos, the gentile is portrayed as being driven by two competing forces:
On the one hand: he longs to get his fingers on every last drop of wine in order to pour it as a libation to idolatry.
On the other hand: he would never do anything that would make him look improper - trespassing into a domain that is not his, or handling something that does not belong to him.
The setting of the mishnah:
A Jew is hosting a gentile in his home; the two are reclining together at the table and drinking wine. In the time of the Mishnah it was customary to place some of the food on the table itself, and some on a side table - a sort of sideboard - from which the hosts would take the food and serve it to the guests. A guest feels comfortable taking what is set on the table in front of him, but he would never get up and go over to the side table and handle what is placed there, since he has no business there.
In the words of the mishnah: "Ha'ochel imo al hashulchan" - a Jew who ate together with a gentile at the same table, "v'hiniach login al hashulchan" - and left one vessel of wine on the table, "v'login al hadulbeki" - and a second vessel of wine on that side table. (In other versions: "gulfeki." This word, in the form "dulfak," even found its way into modern Hebrew, in the sense of a stand.)
"V'hinichan v'yatza":
The host steps out for a short while and leaves the gentile alone at the table. Here the mishnah distinguishes between the two vessels:
"Mah she'al hashulchan asur" - the wine that was left on the table, even though it had been kosher, is presumed to have been handled by the gentile, and he may well have poured a libation from it. For if the Jew were to walk in and find his guest handling this wine, there would be nothing strange about it: the wine is sitting on the table, and a guest is expected to help himself to it. We therefore assume that he did in fact touch it, and the wine becomes forbidden even to derive benefit from.
"U'mah she'al hadulbeki mutar" - as for the wine on the side table: since the guest has no business touching what is set there, and such behavior would be entirely out of place, we assume he would not have done so. This wine therefore remains permitted, even if it was open.
All of this, however, applies when the Jew left with the expectation that his guest would stay where he was.
"V'im amar lo hevei mozeg v'shoteh":
If, as he was leaving, the Jew said to him, "Pour for yourself and drink" - that is, mix the wine and water for yourself as you are accustomed to do and drink, which in effect means: help yourself - the ruling changes:
The wine on the side table: it too is regarded as having been touched by the gentile, since now he would feel comfortable helping himself to it; and if the Jew were to come in and catch him, he would answer, "You told me I could help myself to a drink, and I assumed you meant this one as well."
Any open wine in the house: any vessel of wine located anywhere the guest can reach - we must assume that he will get up, go over and touch it in order to pour a libation from it, as long as he has access to it. For if he is caught, he will say, "I understood that you meant for me to help myself, and I assumed you meant this wine too, so I tasted it," or any other excuse. All the open wine is therefore forbidden.
Even sealed and stoppered wine: if the Jew stayed out of the house long enough for the gentile to remove the seal from the wine entirely, insert his fingers and pour a libation, reseal it, and let the seal dry, this wine too becomes forbidden. This measure of time was already explained in the earlier mishnayos, except that here the mishnah adopts it as the standard view, without mentioning the other opinions cited there.
In summary: Our Mishnah distinguishes between wine that is set on the table, which the guest is free to take and which is therefore forbidden, and wine that is set on the dulbeki (the side table), which is none of the guest's business and is therefore permitted. But once the host has said to him "hevei mozeig veshoseh" - "pour yourself a drink," the guest may touch whatever comes to hand and can protect his dignity with a reasonable explanation for his actions - and therefore we must suspect that he indeed did everything described, wherever this is reasonably possible.