Read this from the same link:
Originally Posted by TurtleDude
Many Historical Accounts:
The guillotine was invented as a humane and painless method of execution, one that brought an instant death: could the inventors have been wrong? Plenty of anecdotes have been used by all sides, many of them dating from the French Revolution, one of the guillotine's most prolific periods. Scientists who asked their students to watch and record how many times they blinked (the scientists themselves being guillotined), murderers who tried to speak, and rivals who bit each other while their heads were in a bag; all have been cited at some point. One famous tale concerns Charlotte Corday, the killer of Marat, whose cheek supposedly reddened after the executioner slapped it even though, at that point, she was just a severed head being held up to the crowd.