Rashi's secret TB Khullin11-12

Dappim TB Khullin 11-12 discusses the role of presumptive majority status when determining halakha. “From where is this matter that the Sages stated: Follow the majority, derived? The Gemara is surprised at the question: From where do we derive it? Obviously, it is derived from a verse, as it is written explicitly: “After the majority to incline” (Exodus 23:2). The Gemara explains: With regard to a majority that is quantifiable before us (רוּבָא דְאִיתָא קַמַן), for example, in the case of a piece of meat that was found on the street before ten shops, nine shops selling kosher meat and one shop selling non-kosher meat, one follows the majority and deems that piece kosher. Or when the Sanhedrin adjudicates a case, one follows a majority of the judges in determining the ruling. In these cases, we do not raise the dilemma.” (Sefaria.com translation)

The Gemara wants to know the source of a statistical majority (רוּבָא דְלֵיתֵיהּ קַמַן) like “the case of a minor boy and a minor girl. If the boy entered into levirate marriage with the girl, it is permitted for them to remain married, and there is no concern that when they grow older it will be discovered that the boy or the girl never develop sexually. Rather, one follows the majority, that minors develop sexually at puberty.” (Sefaria.com translation)

10 different sages provide proof texts from the Torah. Each one is not completely convincing as the source of a statistical majority. Rashi ד"ה פסח provides two possible sources for a statistical majority. His first answer is it is a halakha transmitted to Moses from Sinai. His second answer is that a statistical majority is just a sub category of a majority that is quantifiable before us. He writes that we rely on these assumptions and don’t have to check the 18 possible ways an animal can become trief. We only have to check the lungs because a defect there is more common. We don’t have to check the other possible scenarios an animal can become trief because we rely upon Rav Hunah who holds that an slaughtered animal by a shokhet is under the presumption of it being permitted. (TB Khullin 10)

And Rashi concludes “Nevertheless, we don’t publicize this.” Now you know Rashi secret.