A unique mechanism involving a huge, slanted blade, pulleys and a hinged neck harness was effectively meant to cause instant death.
But this ‘humane’ approach was often called into question, with fears that the swift impact actually caused pain and suffering.
Decapitation was so swift, that the brain might take a few seconds to register decapitation, medics argued.
Post-mortems often revealed eyelids moving up and down, and that faces quivered. more... A recorded instance may be this one, of Charlotte Corday l'ange de l'assassinat ...Charlotte was executed on 17 July 1793. Legend has it that after she was guillotined the executioner took her by the hair and slapped her across the face. Her face scowled at the executioner in "unequivocal indignation"! The slap was considered an unacceptable breach of etiquette and the executioner was locked away for 3 months...
Thanks to Elena-Maria for this article and link.
The Death of Louis XVI.
The Death of Marie-Antoinette.
Here is the Instument of Death
*It is also said, although a guillotine was not used but a sword, that Anne Boleyn blinked at the spectators and her mouth moved as if to speak.