EggWalrus is right, but I'd use lopping shears (bigger, longer handles) instead of pruning shears or kitchen shears. I've done it with loppers (once) and it was ok, seemed like bird got spooked by them. Now I hang the bird, either in a cone or just by the feet with a cord, and let it calm down a minute or so. Then I use a utility knife with a new blade, hold the head in one hand, work the blade down to the skin and quick slice. Be sure to avoid the feathers, they are like armor. With the head in your hand, it's dark for them and they seem not to struggle. Then, walk away for a few minutes, wipe off the blade, get a drink of water, come back and it's dead.