She recommends using a sealable box, like tupperware, and a separate container inside it with baking soda and vinegar. You set up the baking soda in the separate box, with a trial run to make sure it doesn't overflow when you add the vinegar. Then you put the box of baking soda into the tupperware box, add the chick to the dry area of the tupperware box, add the vinegar to the baking soda, and close the box quickly. The reaction of baking soda and vinegar makes carbon dioxide. This knocks out the chick quickly. It does struggle to breathe for a bit and may thrash briefly, but it's probably unconscious by then, and is dead shortly after. I think it's more humane and less traumatic for the chick, and for me, too.