(Q) Principle:

 

(A) The final hammer blow is an example of completing a utensil, making it fit for use. This creative activity is forbidden only when one “creates” something that wasn’t there before, such as opening a shirt at the neck to allow the head to go in. (the final step of manufacturing a shirt) It is not forbidden, however, to cut open a sealed barrel to get its contents, since the barrel and its seal are two different items that were connected. Here, The opening was not created, it was, merely, “revealed” The barrel had an opening already from before, it was just covered.

 

     *Connection: Same author (Rav Yehudah) as sugya 1 and 2. (And Rav Kahana asking questions)*