this can be explained in accordance with the explanation of Rabbi Zeira that dough is different because it is enhanced in any event, come and hear a refutation of that explanation from the latter clause of the same baraita: Forbidden wine that fell into lentils or forbidden vinegar that fell into split beans renders the food forbidden. And Rabbi Shimon deems them permitted. And here also, it is a case where the forbidden substance detracted from the flavor of the dough from the outset, and they disagree.

And if you would say: Here too, it can be explained as Ulla responded to Rabbi Ḥagga, that the baraita is referring to a case when the vinegar enhanced the flavor of the split beans and subsequently detracted from it, e.g., where it spilled into cold split beans and then they were heated, this cannot be said, as do they actually disagree in a case when the forbidden substance enhanced the flavor of the permitted food and subsequently detracted from it? But isn’t it taught in the first clause of the baraita that if the leaven of teruma fell in first, before the non-sacred leaven, everyone agrees that it renders the dough forbidden, as it enhanced the flavor of the dough at the outset, even though the flavor was subsequently detracted from by the non-sacred leaven?

Rather, must one not conclude from it that the dispute is with regard to a case where the forbidden substance detracted from the flavor of the food from the outset? The Gemara affirms: Conclude from it that this is so.

The Gemara asks: With regard to those three clauses that the baraita teaches concerning different cases, why do I need all three of them? Granted, the last clause, concerning the wine spilling into the lentils, teaches us that the dispute is with regard to a case where the forbidden substance detracts from the flavor of the food from the outset. The middle clause, with regard to the case where the leaven of teruma fell in first, also teaches a novel halakha, which is that in the case of a forbidden substance that enhanced the flavor of the food and subsequently detracted from it, everyone agrees that the mixture is forbidden.

But why do I need the first clause, concerning the case of non-sacred leaven and leaven of teruma falling into the dough together? It could have been inferred from the other two clauses that the dough is forbidden, in the following manner: Now that in the case of the last clause, where the forbidden substance does not enhance the permitted food at all, the Rabbis deem it forbidden, is it necessary to say that it is forbidden in the first clause, where the forbidden substance enhances the food’s flavor at first before detracting from it?

Abaye said: The first clause is necessary to teach that Rabbi Shimon deems it permitted. And this is what the Rabbis said to Rabbi Shimon: This dough was fit to become leavened in two hours if the permitted leaven had fallen into it alone. What caused it to become leavened in one hour? The forbidden leaven. Therefore, the dough is forbidden.

And Rabbi Shimon could respond that when the two types of leaven enhanced the flavor of the dough, they both enhanced it, not only the forbidden leaven; and when they subsequently detracted from it, they both detracted from it. Therefore, it is permitted.

The Gemara asks: Even according to the opinion of Rabbi Shimon, let the permitted leaven and the forbidden leaven combine together and render the dough forbidden, since Rabbi Shimon concedes that if the permitted food was initially enhanced by the forbidden substance it is forbidden.

The Gemara responds: Rabbi Shimon conforms to his standard line of reasoning, as he says that even a forbidden substance and another forbidden substance do not combine to render a mixture forbidden. Accordingly, a forbidden substance and a permitted substance certainly do not.

The Gemara comments: This is as we learned in a mishna (Me’ila 18a): If orla and diverse kinds planted in a vineyard fell into a permitted substance, and neither one is sufficient in its own quantity to render the mixture forbidden, they combine to render it forbidden if together they are of a sufficient quantity. Rabbi Shimon says: They do not combine, and each forbidden substance is treated individually. Here too, since when the forbidden leaven enhanced the dough, it was not sufficient to enhance it by itself, the permitted leaven does not combine with it to render the dough forbidden.

§ The Gemara recounts an incident involving a certain mouse that fell into a barrel of beer. Rav deemed that barrel of beer forbidden. The Sages said before Rav Sheshet: Shall we say that Rav maintains that even in a case where the forbidden substance imparts flavor to the detriment of the mixture, it is forbidden? Presumably, the mouse imparted flavor to the detriment of the beer.

Rav Sheshet said to them: Rav generally maintains that in a case where the forbidden substance imparts flavor to the detriment of the mixture, it is permitted. But here, in the case of a mouse, it is a novelty that the Torah prohibits the flavor from a mouse at all, as it is repulsive and people distance themselves from consuming it, and even so the Merciful One prohibits it. Therefore, although it imparts flavor to the detriment of the mixture, it is still forbidden.

The Sages said to Rav Sheshet: If that is so, that the halakha with regard to a mouse is considered a novelty and is therefore understood to be more stringent than the norm, then a dead mouse should impart ritual impurity whether it is moist or dried out. Why did we learn in a mishna (Nidda 54b) that carcasses of creeping animals impart impurity when they are moist but do not impart impurity when they are dried out?

Rav Sheshet responded: And according to your reasoning, in which you compare the halakhot of ritual impurity to forbidden foods, then with regard to semen, which is also repulsive, it should impart impurity whether moist or dried out. Why did we learn in a mishna (Nidda 54b) that semen imparts impurity when it is moist but it does not impart impurity when it is dried out?

Rather, what have you to say? With regard to the ritual impurity of semen, the Merciful One states: “The flow of seed” (Leviticus 15:16), meaning that the reference is to semen that is fit to fertilize. Here too, with regard to the ritual impurity of a mouse, the verse states: “When they have died” (Leviticus 11:32). The Merciful One states that the carcasses of creeping animals impart impurity only when they are similar to their state at time of their death, i.e., when they are still moist. Therefore, there is no contradiction to the claim that the prohibition against eating a mouse is a novelty and consequently applies even when it detracted from the flavor of the food into which it fell.

Rav Shimi of Neharde’a objects to the assumption that a mouse is repulsive: And is it repulsive? But isn’t it served at the table of kings and considered a delicacy? Rav Shimi of Neharde’a said in clarification: This is not difficult. This statement, that a mouse is served as a delicacy, is stated with regard to a field mouse, and that statement, that it is repulsive, is stated with regard to a city mouse.

Rava said: The halakha is that if the forbidden substance imparts flavor to the detriment of the mixture, it is permitted. But with regard to a mouse that fell into a barrel of beer, I do not know what the reason was that Rav deemed it forbidden. I do not know whether it was because he maintains that if the forbidden substance imparts flavor to the detriment of the mixture it is forbidden, and if so, the halakha is not in accordance with his opinion, or whether it was because although he maintains that if the forbidden substance imparts flavor to the detriment of the mixture it is permitted, a mouse that falls into beer enhances its flavor.

A dilemma was raised before the Sages: