Sorry for the gruesome subject matter, but my post on foreign law and methods of execution brings to mind the practices used in one of the countries popular among the Justices who favor looking to foreign law: France, or as Justice Breyer would put it, La République Française.

  Wikipedia has a fascinating history of methods of execution in France. It seems that from 1792 to 1981, when France abolished capital punishment, the only allowed method of execution was the Guillotine. The Guillotine was originally designed in the late 18th Century to be a more humane method of execution: the idea was that it would be fast, painless, and certain.

The basis for the machine's success was the belief that it was a humane form of execution, contrasting with the methods used in pre-revolutionary, ancien régime (former regime) France. In France, before the guillotine, members of the nobility were beheaded with a sword or axe, while commoners were usually hanged, a form of death that could take minutes or longer - other more gruesome methods of executions were also used, such as the wheel, burning at the stake, etc. In the case of decapitation, it also sometimes took repeated blows to sever the head completely. The condemned or the family of the condemned would sometimes pay the executioner to ensure that the blade was sharp in order to provide for a quick and relatively painless death.

  However, it seems that the use of the Guillotine was plagued by concerns that it was not as swift and painless as it was designed to be. Critics argued that in fact those executed by the Guillotine suffered greatly in the seconds after the blade fell:

From its first use, there has been debate as to whether the guillotine always provided as swift a death as Dr Guillotin hoped. . . . . [in light of] the possibility that the very swiftness of the guillotine only prolonged the victim's suffering. The blade cuts quickly enough so that there is relatively little impact on the brain case, and perhaps less likelihood of immediate unconsciousness than with a more violent decapitation, or long-drop hanging.

Audiences to guillotinings told numerous stories of blinking eyelids, moving eyes, movement of the mouth, even an expression of "unequivocal indignation" on the face of the decapitated Charlotte Corday when her cheek was slapped. Anatomists and other scientists in several countries have tried to perform more definitive experiments on severed human heads as recently as 1956. Inevitably the evidence is only anecdotal. What appears to be a head responding to the sound of its name, or to the pain of a pinprick, may be only random muscle twitching or automatic reflex action, with no awareness involved. At worst, it seems that the massive drop in cerebral blood pressure would cause a victim to lose consciousness in several seconds.

Anyway, that's Wikipedia's take; I don't know how accurate it is.