I find it amusing and a bit revolting that we use humane standards by which we execute the animals that end up in our bellies but not to the people we kill to deter and prevent crime. I'm unsure as to the exact method, but isn't it something along the lines of blunt trauma to the skull or stunning by electricity followed by a slit throat? Sounds pretty painless if the blow actually knocks the animal unconscious. Then we have the death penalty: Lethal injection, electrocution, hanging, firing squad, and the gas chamber. One of these options seems 100% humane (assuming the bullet actually goes to the brain). The rest have the potential to possibly cause unimaginable pain and suffering.
I get that the death penalty is supposed to be a deterrent (it isn't), but you would think we could at least extend the same common courtesy to the people we kill that we extend our food supply.