Continuing from yesterday's post, we asked why one may not interrupt tefilah if a snake wraps itself around one's foot -- even though most snakes don't bite, ain holchin b'pikuach nefesh achar harov, halacha is suspended for even the slightest chance of mortal danger. How is this case different than a case of a person trapped under an avalanche on Shabbos where we are permitted to dig the body out even if there is only a slight chance the person is alive or Jewish.
R' Elchanan answers this question using the principle we mentioned on Monday of shomeir mitzvah lo yeidah davar ra, one who is engaged in the performance of a mitzvah is protected from harm. Really, be it snakes which don't often bite, or be it scorpions which do bite and kill, a person should not interrupt tefilah because the act of being engaged in a mitzvah is the best protection from harm. However, the gemara tells us that this protection is not absolute. Where shchi'ach hezeika, where danger is prevalent and common, the elevated level of danger overrides the protection afforded by the mitzvah. Therefore, we rely on the protection of tefilah with respect to snakes because they are not usually dangerous, but would be permitted to interrupt tefilah to brush off a scorpion.
A more "lomdish" answer to this question is perhaps possible. In the case of an avalanche, the situation that presents itself is one that is clearly life threatening -- the only question is whose life (Jew or non-Jew) is in jeapordy or whether the victim has already perished. However, in the situation of the snake, based on a consideration of most snake's behavior there is no clear and present danger. As an analogy, consider the ruling of the Rambam (Shvisas Asor 2:8) that where a there is a conflict of opinion between doctors over whether fasting on Yom Kippur would endanger a person's health we follow the opinion of the majority. Why in this case do we not utilize the principle of ain holchin b'pikuach nefesh achar harov? R' Scheinberg (Mishmeres Chaim III:Y"K 2) answers by also distinguishing between whether the issue is determining whether danger is present, in which case we follow rov, and whether the danger exists and we just need to determine details, in which case we ignore rov.
The logic behind this distinction can be explained using R' Shimon Shkop's reasoning in Sha'rei Yosher 4:13. The reason pikuach nefesh overrides rov is because the principle of following rov is itself just a din like any other -- pikuach nefesh overrides all halachos, including the halacha of rov. However, where it remains to be determined if danger exists, then we cannot yet call upon the rule of pikuach nefesh to push away the principle of rov because the existance of pikuach nefesh is itself what is at question.
A final solution to this question which may work is to distinguish between types of rov. The rov that presents itself in trying to determine who is buried under an avalanche is based on a statistical evaluation of the residents of the city -- a ruba d'isa kaman, a rov build around observation or counting. The rov that tells us that snakes don't bite is not determined based on observing all snakes in the world, but is rather based on inductive reasoning -- a ruba d'leisa kaman. Perhaps ain holchin b'pikuach nefesh achar harov would apply to a ruba d'isa kaman where a safeik still exists, but not to a ruba d'leisa kaman which essentially resolves a safeik entirely and renders all doubt non-existant (see Shev Shmaytza 2:15)