It's hard to botch execution by guillotine. The last execution by guillotine was likely in France, that used the contraption until they abolished non-military death penalties I think in the late '70's. The French kept it around long enough to chop a few war-time collaborators.
The British used the German State of Hanover's guillotine to execute some "werewolves"-- Nazis dead-enders that tried to play terrorists in the British zone of occupation and murdered some folks right after WW2. The Brits used local civilian law to punish murderers, refusing to make it a war crime or a military offense. When self-government was restored in West Germany, the Germans did away with the civilian death penalty.
In the American South, we used to have an occasional "bad" hanging. Typically, the hangman miscalculated (or didn't bother to calculate) the proper drop, and the process yanked the prisoner's head off like a chicken having its neck wringed. That is apparently what happened to the late Saddam Hussein.
I am of the school that believes that a civilian execution shouldn't be calm or clean. If it's supposed to deter, then public and gruesome is better. As I understand it, a guillotining or a bad hanging will cause a corpse to pretty much dump its entire blood supply on the spot.
