Yeah also if you read about the history of anesthesia and how tissue damage can cause circulatory shock/stress. It makes you think more about the process
It kind of hard to really find the painless/least painful method cause the evidence is not enough since people who gone through the whole process and successfully ctb cant come back and tell their experience.
For now it seems barbiturate, F, morphine, blood choke is the least painful.
And maybe inert gas. But they still have to combine it with sedative though. Also co2 has mix result.