Question

Kiddushin 25a: there is an incident involving Rabbi’s maidservant who immersed, and there was a bone between her teeth, so Rabbi required her to immerse again, because we require even a place that is fit for water to enter, in accordance with Rabbi Zeira’s principle that anything fit for mixing, etc.
It’s not so clear to me what the connection to Rabbi Zeira is. And why do we need a place that is fit for water to enter?a0
I thought of an explanation. What does the Rabbi think?
The law of “interposition” does not mean that the “water” did not reach this “part” of the body. The objects in the mikveh (which are what we are discussing, and they are completely indivisible) are the “person” immersing and the “mikveh.”
A person who immerses is made up of many body parts that together create the identity of a person, and a mikveh is made up of many water molecules that together create a mikveh. But a mikveh is a “place,” not a collection of drops. And a person is a “person”  not a collection of parts.
Therefore, a “person” who enters a “mikveh” but does not enter in a complete way is not defined as having immersed; he is not defined as “coming into the water”  into the mikveh  in the complete sense. (Maybe Sefer HaChinukh 173 would help here.)
Even if the interposition is not in a place that the water actually has to reach, still, this potential interposition between him and that hidden place  if he were to allow the water to enter there (the water that creates the identity of the place and its essence)  removes from him the status of “one who immerses” and “one who comes into the water.” He did not enter the water completely. He entered with additional objects.
This is exactly what the one who disagrees with Rabbi Zeira disputes  there is no “potential” here. Whatever comes, comes. Whatever comes  welcome.
What does not now need to be reached does not need to be reached in any way.
There may be a certain novelty here: there is no need for water to enter as an act of “water entering,” but rather as a test of complete entry into the mikveh.