“It’s painless and works every time.”
I always am skeptical of statements that say (1) how terribly painful a particular way to die is and (2) how painless another way is. Noone but One who has died by any method of execution has come back. And He didn’t dwell on that subject.
Nitrogen asphyxia is a common industrial accident. The victims don’t even know their dying until its too late.
L
Carbon monoxide is completely painless. It bonds with red blood cells like CO2 does, but does not unbond. You just get sleepy.
That would be my preference to die if I was so sentenced.