Piano wire might be too quick. This should be drawn out for awhile. Burning at the stake comes to mind.
They buried him up to his neck, with a serrated bamboo saw attached to his neck. The Village Women would come by and pull the saw one direction and then the other in a slow and deliberate way. Eventually, the man died, but it took a very long time.
I think it was the definition of the term, “death by a thousand cuts”. Of course, the part of the Novel where they boiled the English Sailor alive wasn't too pretty.