To fast, just tie him to a chair and inject him with battery acid.
Wait 10 seconds, then cut him loose and watch him bounce.
Actually, I must correct you on the erroneous perception of the iron maiden.
It was a wickedly cruel device in that the spike inside were placed in such a way to pierce some of the most painful areas of the body, such as the eyes, the bladder, the base of the penis and other places where you never ever want to have a spike, yet none of the wounds are fatal.
Also, with having two doors, one main door and one for the face, you could open one while leaving the other closed, so the person inside would still be locked in place by spikes, and then the open door could be closed again thus piercing all of the wounds again.
And it goes on like that until they expire days later.
And they have to stand the whole time.
Good but still to fast. Stake his naked butt out over a big azz ant hill......and then it’s go ants GO!!!!