I was reading the post about clean killing of chicks a while back and saw the baking soda/vinegar method My first thought was, that's easy. Then I thought about it some more.
Suffocation is generally considered a bad a traumatic way to die. Oxygen runs out and the CO2 levels rise.
Suffocation happens with inert gases without anyone noticing it happen. It is an extremely rare occurrence in nature and we have no warning detection system. Inert gases and carbon monoxide both fall into this category.
What oxygen breathing, carbon dioxide exhaling creatures do have a mechanism to detect is high levels of what we exhale. CO2.
Rising levels of CO2 cause rising levels of panic, as the body recognizes a threat to life and tries to get away.
So this is about as distressing to the animal as it is possible to be I'd rate it with drowning in terms of panic and pain.
I'm preparing to get a round of chicks again after a long time and have been considering all the factors involved I've never had to kill chicks before, but I have killed mature chickens and ducks. I've done both throat slitting with the bird in a cone and neck breaking by hand. In neither case was there any sign of struggle or panic
When you do have to kill, be kind. Pet the bird, give it a treat, then do the deed calmly and fast. There will be a moment of pain, but is is over quickly and without trauma.
I think I prefer the neck breaking, because once when I had to kill a number of chickens, I came back lather from letting them drain and found one was still alive. I never want that to happen again.
After a meat bird is dead, I generally let it hang for a day or so, then pluck it, I just don't like the feeling of rushing the butchering process if I have a choice. I like to give the bird a chance to be dead, let the body grow cold and give your own mind a chance to accept the fact. Then you can move on to making the best meal ever from what the chicken left behind.
I hope this information was helpful
Finula in Pittsbugh