Shabbos Daf 146 שבת דַף 146

The next Mishnah in the perek states that one may use a sword to break open a barrel to eat dried figs from it, בלבד שלא יתכוין לעשות כלי - provided that he does not intend to make a vessel, through creating a proper hole in the barrel. Rashi explains that breaking open the barrel without any intention to make it into a vessel, is an act of מקלקל - destruction, which is permitted on Shabbos.

The Gemara clarifies that the Mishnah only permits breaking  the barrel for pressed figs, not loose figs. This, says the Gemara goes according to Rebbe Nechemiah who holds, אין כלי ניטל אלא לתשמיש המיוחד לה – a utensil is only permitted to be moved if one is moving it to use for its specialized purpose. Rashi explains that since the person requires the sword to separate the pressed figs, it is permitted to use the sword to open the barrel, as well. If the figs in the barrel are loose, however, then the sword is not required for its usual purpose (meaning to cut the figs apart) and therefore it is prohibited to move.

Rabbah said דבר תורה כל פתח שאינו עשוי להכניס ולהוציא אינו פתח – As a matter of Torah  law, any opening that is not made for the purpose of bringing things in and taking things out, is not deemed a true opening and therefore one is not liable for its creation. The Rabbanon, however, prohibited even one-way openings because of the case of chicken coops.

The purpose of a hole in a chicken coop is both to allow air to enter, and also to let lethal vapors escape. Since many people are not aware of the second reason, they will think that the hole is only in order to let air enter and they will conclude that it is permitted to make a hole in the chicken coop. Therefore, the Rabbanon prohibited even one-way openings.

It was stated in a Baraisa that all agree that it is permissible to reopen an old hole in a cask. Rav Yehudah said in the name of Shmuel that this Baraisa was referring only to holes that were plugged in a place where it was meant לשמר - to preserve the aroma of the wine, but not in a place לחזק - where it was meant to strengthen the cask.

Rashi explains that since  a plug used to keep the vapors from escaping (לשמר) was quite flimsy, the cask remains with the status of a perforated vessel. Reopening the vessel is therefore permissible. This is in contrast to a plug used to ensure that wine does not flow out (לחזק). Since this plug creates a complete seal, it erases from a legal standpoint, the existence of the perforation. Removing the seal is therefore forbidden as it is tantamount to creating a new opening.