Pesachim 9B

ובא כהן והציץ בו לידע אם זכר הוא אם נקבה היא. ובא מעשה לפני חכמים, וטיהרוהו, מפני שחולדה וברדלס מצויין שם.

and a priest came and glanced at the baby to ascertain whether it is male or whether it is female, as a woman who has just given birth, even to a stillborn, is ritually impure for different lengths of time, depending on whether she gave birth to a male or a female (see Leviticus 12). And the incident came before the rabbis, to rule whether or not the priest contracted ritual impurity when standing over the corpse, and they deemed him ritually pure. The basis for this ruling was due to the fact that as a marten and a polecat [bardelas] are found there, it is likely that the baby was dragged away before the priest arrived at the pit.

והא הכא ⁠— דודאי הטילה, וספק גררוהו וספק לא גררוהו ההיא שעתא, וקאתי ספק ומוציא מידי ודאי! לא תימא ״שהטילה נפל לבור״, אלא אימא: ״שהפילה כמין נפל לבור״, והוי ספק וספק.

And yet here, where it is certain that she threw the stillborn baby into the pit, and it is uncertain whether a marten or polecat dragged it away and it is uncertain whether it did not drag it away at that time, the rabbis nevertheless ruled that an uncertainty comes and overrides a certainty. The Talmud rejects this contention: Do not say in the baraita that she certainly threw a stillborn into a pit; rather, say that she threw an object similar to a stillborn into a pit. Perhaps it was not a stillborn baby; it might have simply been congealed blood, which does not transmit impurity. And therefore, this is a conflict between uncertainty and uncertainty. It is unclear whether there was anything in the pit that could have rendered the priest ritually impure, and even if there was, it might have already been dragged away.