- Give them a pill or injection that renders them unconscious.
- Wood chipper. Blunt axes. Lawnmowers. Thrown from helicopter. Torn apart by hungry pigs. It doesn’t matter because the victim is unconscious, and so can’t be said to suffer.
Once they’re unconscious, which can be achieved any number of humane ways, and can’t in itself be viewed as inhumane since we sleep every night (and perform dental work and surgery under anesthesia), anything you do to render them dead is humane because they don’t experience it. And were I on death row and my execution came up, and I was given a pill and told “take this so you won’t be awake to be executed,” I don’t think I’d hesitate.