Well at least in that comment, I can see your misunderstanding. Human beings are in fact mammals, as such, comparing them metabolically (in this instance for the purposes of euthanasia*) seems perfectly reasonable to me. You are free to disagree but I don't think I'm the one being unreasonable here.
*Let's not get into the semantics of whether applying the death penalty is technically euthanasia, let's just stick with the Oxford dictionary definition:
put (a living being, especially a dog or cat) to death humanely.
My point, which you seem to have overlooked, is that nobody uses a strange and exotic method such as nitrogen gas asphyxiation to either euthanize and animal or as a method of medically assisted suicide. How it came to pass that it was considered a good method for death penalty cases is baffling to me.