Perhaps more than any other single cause, it is the guillotine which inspired the term Reign of Terror, coined to capture the fear which infected revolutionary France from 1792 to 1794.
The nobility and monarchy, in losing their power to the revolutionary mob, also became prey to the Revolutionary Tribunal, led by Robespierre, which not only sentenced legions of aristocrats to beheading by the guillotine, but also ensured that these executions would be public. The fear inspired by the guillotine was legendary (indeed, it has came to be nicknamed 'Madame Guillotine'), but more than the fear of the actual mechanics of the death instrument was the fact that little to no evidence was needed to sentence one to death by it. As long as Robiespierre's tribunal offered the charge of 'Crimes Against Liberty,' then a death sentence was practically written in stone.
The Guillotine, as stated in the Pimpernel, took place in a square called La Place de la revolution. Before the Guillotine, the government used to execute people by breaking them on the wheel (an even more cruel and unusual capital punishment device), but deemed inhumane, the National Assembly instilled the use of the Guillotine after commissioning an instrument of execution whose principal charge would be to simply end life, as opposed to inflict pain. Moreover, because of the guillotine's efficiency, it meant that it could be used for the execution of all classes.
The guillotine itself involves a large, massive blade suspended from a rope on a tall frame, so that the impact severs the head from a body in a swift blow. Many observers at the time of execution claimed that the guillotine didn't end life as swiftly as it promised to -- and that the severed heads blinked and made expressions. Science has yet to prove the validity of these claims.