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8. Doing an action which causes a hole to be made unintentionally:
A. Removing a knife from a barrel:
Due to the [Rabbinical decree against performing any hole in a vessel, whether for entering or exiting] one may not puncture a new hole in a barrel for the wine to flow from [this hole]. [Furthermore] even if it already has a hole and one [simply] wants to add to it and slightly widen it, it is forbidden. [However, in this case it is only forbidden] when one intends to widen the hole, However, if there was a knife jammed in the wooden barrel from before Shabbos in order for the wine to flow from the hole that is formed upon removing the knife, then it is permitted to remove it and reinsert it on Shabbos.
The reason this is allowed: [Now], although it is impossible to avoid the hole from widening upon removing it, [nevertheless] this does not pose any [Halachic] problem since one has no intent to widen the hole. Now, although it is inevitable [for this widening to be avoided, and thus it should be prohibited even if one does not intend to widen it] nevertheless since even one who makes a new similar hole intentionally only transgresses a Rabbinical prohibition, being that [the hole] is only made removing [the wine] out from it [as opposed to also entering wine into it], therefore [the Sages] were not so stringent on this to prohibit even adding to [this type of] hole unintentionally. [This opinion holds that we do not apply the prohibition of Pesik Reishei by an Issur Derabanan.]
Other Opinions: [However,] there are opinions that argue and say that [the Sages] did not permit to remove the knife from the barrel on Shabbos unless one has already removed it once from before Shabbos. [The reason removing it one time before Shabbos suffices is] as then it is no longer inevitable to avoid widening the hole through removing it on Shabbos, and rather it is possible that [removing] it will not add [to the hole] at all, in which case even if it did [happen to] add [to the hole when removed on Shabbos] it poses no [Halachic] problem being that one did not intend to do so.
The Final Ruling: The main [Halachic] opinion is like the former opinion, although in a situation that there is not much need for one to remove the knife, it is proper to suspect for the latter opinion.
B. Removing a knife from a bench and the like:
If the vessel cannot hold 40 Seah: However, a knife which is jammed into a bench or another detached item, is permitted to be removed on Shabbos [according to all opinions] even if it had never been removed beforehand.
The reason for this is: because making a hole in a detached item never carries with it the prohibition of building but rather [can be forbidden] only because of a decree [that one may come to] “fix a vessel” if he makes an opening that is meant for entering or exiting. However, when one is not making an opening at all for entering or exiting but rather it [just happens to] consequently be formed through removing the knife, then there is no prohibition at all in doing so. [This is opposed to the case of a barrel that the making of a hole serves that the wine flow from it, and therefore in that case there are opinions which prohibit one to remove the knife if it will inevitably widen the hole.]
C. Removing a knife from a vessel which is large enough to hold 40 seah:
If [a knife] is jammed into a large barrel or other large vessels which hold 40 seah [and thus] carry with them the building and destroying [prohibition], then it has the same law as if it were jammed stuck in a wall [in which the custom is not to remove on Shabbos unless it had been previously removed before Shabbos].
Summary-May one remove a knife from a vessel which does not hold 40 Seah?
If the knife had been removed one time before Shabbos, then it is permitted to remove it. If not, then if this hole could be used to remove items through it, then it is proper to avoid removing the knife in a case of no need. If the hole would not serve one any purpose, such as a knife that is jammed in a bench that does not hold 40 seah [and is not attached to the ground] then it is always allowed.
 Admur 314:3; Michaber/Rama 314:1
 Admur ibid; Michaber ibid
 Admur ibid; Rama ibid in accordance to opinion of Michaber, as rules the Ravaya and Mordechai [See M”B 314:10]
 Admur ibid; Taz 314:2; M”B 314:11
Opinion of Michaber by Pesik Resihei of Derabana: From this Halacha we see the Michaber rules there is no prohibition of Pesik Resihei by a Rabbinical prohibition. Vetzaruch Iyun as in 320:18 the Michaber argues on the Aruch and rules by a Rabbinical case that one may not do a Pesik Resihei even if Nicha Lei. Vetzaruch Iyun Gadol!
 Admur ibid; Opinion of Rama ibid
 Terumos Hadeshen 64
 Admur ibid; Taz 314:2; M”B 314:11; To note that according to those Poskim that rule in 314:4 that even by a wall there is no prohibition to remove the knife, then certainly here there is no prohibition involved. See M”B ibid]
 Lit. Tov
 Admur 314:5; Michaber 314:12
 Admur 314:5; M”B 314:11
 Admur 314:2
 Admur 313:17; as well as 314:19
 Admur 314:5