Look at the way we treat prisoners who have been found guilty of a capital crime: lethal injection.

That was because drowned, hung, shot, or electrocuted was considered inhumane. Even the first of 3 of the cocktail puts the prisoner to go unconscious.

Now, treat the animals that we eat similar. Nitrogen gas suffocation is known to be the least traumatic death yet. Some executing prisons are going to that as well.