Do you have any links or information on claims that either C02 or drowning is dangerous/traumatizing to centipedes? I have heard one opinion stating it is harmless by an individual who claims have drowned 100's of centipedes. He seemed to making a point to counter the view postulated by others suggesting that it is harmful, but I am yet to see anything substantial to suggest it is, other than people assuming that it must be traumatising because it's drowning and that would be traumatising to us.
Drowning generally is not as harmful to arthropods as humans, since they have a comparatively low metabolic rate and often store air near the spiracles. Ants can go a week underwater, for example. I can't speak to centipedes in particular, however. A similar case is true for carbon dioxide.
I have no evidence, so I spoke out of turn. I've read here (can't remember what threads specifically) that inexperienced keepers can kill their pedes using the drowning method. Definitely speaking from ignorance on this topic, and I think other people just getting into this hobby may also be taken aback by the sexing process. Schmiggle's comment about arthropods reacting differently based on their metabolic rate is very interesting. Like you said, I assumed drowning would be traumatizing because of how it affects humans - but it's good to remember that other species experience the world differently and I can't necessarily attribute my perceptions to others.
