What are the conditions for slaughtering, is permission required for it, and from whom is permission obtained? Is severing the head during slaughtering considered unlawful, and what is its expiation?

No one is permitted to slaughter what does not belong to them, except with the owner's permission. As for separating the head during the slaughter, it is neither forbidden nor does it require expiation. However, it is preferable not to intentionally sever the head at the time of slaughter.