A woman bit her nail a few days before going to the mikva. She was certain that the nail got stuck in between her teeth, but while doing chafififa she could not locate the nail. She went to the mikva.Two weeks later she found the nail inside her mouth and is certain that it is the same nail that was there before the mikva. What is the halacha?
There is no need to go again to the mikva.
The Shulchan Aruch (198:26) rules that even when a lady didn’t check herself before the mikva, but ate meat (for instance) after the mikva, and then found meat between her teeth, she can rely on the fact that she ate meat later.
In this case, the nail was found two weeks later, and therefore we can assume that the woman has bit her nails in between, and there cannot be certainty that this is the same nail. Moreover, she checked before the mikva, and did not find anything, so that the natural assumption is that the nail was not there at the time of immersion.
In addition to this, there is room to discuss whether this is a case of “makpid” (of course, it is a case of mi’ut). The nail, it appears, was there for a very long time without causing being noticed (in fact, it was never noticed, till it emerged by itself), and there is therefore room to consider whether there is a kepeidah.
In addition, most authorities rule that the entire concept of a chatzitzah in beis ha-setarim is only rabbinic.
Therefore, one can be lenient in this case, and not require an additional tevilah.