Sanhedrin Chapter 7, Mishnah 2. The Mishnah continues detailing how Beis Din would execute the different court-imposed death penalties, and now we arrive at the mitzvah of those who are burned - the procedure for carrying out execution by burning. It must be prefaced that although the word 'burning' means being burned, the intention is not burning from the outside like burning at the stake, but rather burning from the inside specifically, as will be explained.
The tension between the severity of the punishment and "love your neighbor as yourself":
The same tension that we have seen again and again applies here as well. The mitzvah of "love your neighbor as yourself" requires choosing a nice death for the condemned man, by minimizing the pain, suffering, and degradation as much as possible, and it is hard to imagine a harsher death than being burned alive in a fire. From here, Chazal learned from Nadav and Avihu, the sons of Aharon, whom the verse testifies were burned even though the burning was only inside their bodies - that an internal burning is also called burning. Once this became clear, Chazal understood that it is better for the condemned man to be burned only from the inside, in terms of the speed of death and the reduction of pain, than to be burned from the outside first. Therefore, the procedure of burning is done from the inside.
The procedure of burning as described by the Mishnah:
"Mitzvas hanisrafin" - this is how they fulfill the mitzvah of executing the condemned man by burning. "Hayu meshake'in oso bezével ad arkuvosav" - they would fix him in his place by burying him in dung up to his knees. The commentators disagree on the nature of this dung:
Tiferes Yisrael: The dung is necessary and intentional, because there is also an element here of degrading the condemned person, since this is a man or woman who committed an extremely severe transgression. And even though in the previous Mishnah great effort was made not to degrade the condemned person, one must distinguish between degrading the corpse after death and humiliating the person while he is still alive, after he has committed a terrible act.
Meiri: There is nothing special about the dung, and regular earth could be used, and the result is the same.
The purpose of the fixing is so that the condemned man will not move when molten metal is poured into his throat, because if he moves, the metal is liable to splash and burn him from the outside, adding to his suffering. Ironically, specifically in order to reduce the suffering and do what is best for him, they try to prevent him from any movement. And even though fixing only the knees and legs does not prevent twisting, we will see immediately that they also restrain him from above.
"Nosen sudar kasheh lesoch harakkah vekorech al tzavaro" - how do they get him to open his mouth? By strangulation. For this purpose, they take two scarves: one hard and rough, which is effective for a strong press, but which is liable to wound and chafe the neck from the outside; and therefore they wrap it in a soft scarf - silk, cotton, or the like - so that it will not chafe and cause pain. They wrap the combined scarf around the neck of the condemned man.
"Zeh moshech etzlo vezeh moshech etzlo" - the witnesses are the ones pulling, since the witnesses are the ones who carry out the execution in all cases, and as we saw in the previous Mishnah that they are the ones who push and drop the stone. Here too, the two witnesses pull on the two ends of the scarf and strangle him, "ad sheposei'ach es piv" - until the condemned man's mouth opens and he can receive the molten metal.
Here the Mishnah goes back a bit: "Umasich es hapesilah" - they prepared a fire and melted the wick, a metal bar that is mostly lead and sometimes tin. "Vezorkah lesoch piv" - once the condemned man's mouth has opened, one of the witnesses pours the molten lead into his throat. "Yoredes lesoch me'av vechomeres es me'av" - it goes down into his intestines and burns him from the inside, roasting his internal organs.
The opinion of Rabbi Yehudah:
Rabbi Yehudah opposes the strangulation that preceded the pouring. His concern is that the will to live might grow stronger in the condemned man and he will not open his mouth, and from the strangulation he will die of asphyxiation - and it turns out that a man whose sentence is death by burning died by strangulation, and the mitzvah was not fulfilled in him. For this reason, in his opinion, one must not risk killing him by pressing his neck, but rather one must open his mouth by force. And these are the words of the Mishnah: "Rabbi Yehudah omer, af hu im mes beyadam" - if he dies by their hands, meaning because of the strangulation, "lo hayu mekaymin bo mitzvas sereifah" - the mitzvah of burning will not have been fulfilled in him.
"Ela poschin es piv bitzvas shelo b'tovaso" - Rather, they force his mouth open with an instrument, such as tongs or the like, against his will; and although this is unpleasant, it ensures that he dies the death designated for him. "Umadlik es hapesilah vezorkah lesoch piv, veyoredes lesoch me'av vechomeres es me'av" - And the continuation repeats what was stated above: the rest of the process is identical, and once his mouth is forced open, they pour the molten lead into his throat and it burns him from the inside.
The Opinion of Rabbi Elazar b'Rebbi Tzadok:
Rabbi Elazar b'Rebbi Tzadok completely rejects this method of execution by internal burning, and understands the verse according to its simple meaning - literal burning, by placing the person into a fire. "Maaseh bevas kohen achas shezinsah" - There was an incident involving a daughter of a kohen who committed adultery, whose punishment is burning, "vehikifuha chavilei zemoros vesarafuha" - they surrounded her with bundles of branches and burned her alive. Here we see burning from the outside, and from this precedent he argues with the approach of the Mishnah.
"Amru lo, mipnei shebeis din shel osah shaah lo hayah baki" - The Sages answered him that the beis din that burned the woman alive did not know the halachah and was not expert in it. The Gemara adds that they were Tzedukim. The Tzedukim were a faction within the Jewish people who denied the Oral Torah and read the verses literally, and did not practice mitzvah observance; and based on this literal reading, they thought that burning meant burning from the outside. However, the Sages stated that this is not the tradition we possess, but rather the burning is done from the inside, and therefore they completely rejected this proof.
In summary: Our Mishnah teaches that the mitzvah of those sentenced to burning is fulfilled specifically through internal burning, based on the derivation from Nadav and Avihu and the obligation to select a favorable death for the condemned. The order of events is as follows: sinking him in manure up to the knees to secure the body, wrapping a rough cloth inside a soft cloth around his neck, the two witnesses pulling on the ends until his mouth opens, and pouring the molten wick into his mouth, which burns his intestines. Rabbi Yehudah is concerned that he might die of strangulation and therefore instructs to force his mouth open with tongs against his will, and Rabbi Elazar b'Rebbi Tzadok sought to prove from the burning of the daughter of the kohen that burning is literal - and his proof was rejected, since that beis din was not expert. As a matter of halachah, although this is not practiced in actuality, the ruling follows the opinion of the Sages: strangulation with a cloth and internal burning.