Resh Lakish said in the name of Levi the Elder, "The act of shechitah counts at the end," but Rabbi Yochanan said that the complete process of the cut, from the beginning untill end end, is called shechitah. For example, if someone started the shechitah while outside the Temple and completed it inside, then according to Rabbi Yochanan he is liable for bringing sacrifices outside the Temple, since from the beginning of the cut he was already doing the shechitah. According to Resh Lakish, he is not liable, since only the end of shechitah is significant, and that happened inside.
Rav Yehudah said in the name of Rav, “If one severs the pipe in two or three places, his slaughter is valid.” But when he repeated this teaching in front of Shmuel, Shmuel said it was invalid. A defense for Rav: as we will learn later, two people can hold a knife and together make a shechitah to an animal. This proves that you can make two cuts! Answers Shmuel, “No! They are holding the same knife together and cutting. We need a clearly visible single cut.”
Art: Caspar David Friedrich - Two men at moonrise by the sea