Zevachim 74B

מאי שנא שלשה דאיכא רובא? שנים נמי איכא רובא! מאי שלשה דקתני ⁠– תרתי והוא.

The Talmud asks: What is different about a case where the pomegranate fell into a group of 3 other pomegranates? The essential factor is that there is a majority of permitted pomegranates, which nullify the pomegranate that fell from the 10,000. Even if it fell into a group of two others, there is a majority of permitted items. Why must it fall into a group of 3? The Talmud explains: What is the meaning of 3 that the tanna of this baraita teaches? It means that there were two permitted pomegranates initially, and the pomegranate of uncertain status fell into them, for a total of 3.

ואיבעית אימא: סבר לה כרבי אליעזר.

The Talmud returns to the question concerning the opinion of which tanna is followed by Shmuel, who is stringent with regard to a compound uncertainty involving idol worship. And if you wish, say instead that Shmuel holds in accordance with the opinion of R' Eliezer, as he is similarly stringent with regard to mixtures of items of idol worship, as explained in tractate Avoda Zara (49b).

אמר ריש לקיש: חבית של תרומה שנתערבה במאה חביות, ונפלה אחת מהן לים המלח ⁠– הותרו כולן; דאמרינן: הך דנפל ⁠– דאיסורא נפל.

§ The Talmud discusses a related topic. Reish Lakish says: In the case of a jug of teruma produce, which may be eaten only by a priest and his household, that was intermingled with 100 jugs of non-sacred produce, they are all considered as teruma, as a sealed jug is significant and is not nullified. And if one of these jugs fell into the Dead Sea, all the jugs are permitted, as we say: Since there is that jug that fell, the assumption is that it is the prohibited jug that fell.