Many sources refer to the story of Robespierre having been guillotined
face-up as a legend. He is reported to have uttered a blood-curdling
scream, but this was a reaction to the pain of having a bandage ripped
off his freshly-mangled jaw.
From "The Terror: The Merciless War for Freedom in Revolutionary
France," by David Andress:
"The scene at the Terror's conclusion was just as striking. Having
struck fear into every heart, Robespierre was seized by men who were
terrified that they too would be killed if they did not act at once.
During that night the Jacobins lost their nerve and melted from view
as Robespierre and his collaborators were captured. During the seizure
Robespierre was shot in the jaw, probably in a botched suicide, and
then led to the guillotine with bandages around his head. The bandages
blocked his head from fitting into the execution machine, so they were
ripped off. The head went into its stock. The blade was raised for its
fall. Robespierre began to scream, a terrible, unforgettable cry that
was to live in nightmares until it suddenly stopped."
Telling It: Craft is Critical
Probably the best-known history of the French Revolution is that of
Thomas Carlyle. Here's his description of the death of Robespierre:
"All eyes are on Robespierre's Tumbril, where he, his jaw bound in
dirty linen, with his half-dead Brother, and half-dead Henriot, lie
shattered; their 'seventeen hours' of agony about to end. The
Gendarmes point their swords at him, to shew the people which is he. A
woman springs on the Tumbril; clutching the side of it with one hand;
waving the other Sibyl-like; and exclaims: 'The death of thee gladdens
my very heart, m'enivre de joie;' Robespierre opened his eyes;
'Scelerat, go down to Hell, with the curses of all wives and
mothers!'--At the foot of the scaffold, they stretched him on the
ground till his turn came. Lifted aloft, his eyes again opened; caught
the bloody axe. Samson wrenched the coat off him; wrenched the dirty
linen from his jaw: the jaw fell powerless, there burst from him a
cry;--hideous to hear and see."
The French Revolution, A History by Thomas Carlyle
This isn't proof, but note that in the famous Beys depiction of "The
Death of Robespierre," the subject is shown in a face-down position:
Amazon: The Death of Robespierre 28th July 1794
I browsed through several reputable biographies of Robespierre (thanks
to Amazon's "Search Inside the Book" feature), and not one of them
recounted the face-up legend. If I were the Snopes Urban Legends
Reference Pages of the 18th Century, I think I'd call the face-up
guillotining of Robespierre "unproven."
My Google search strategy:
Google Web Search: robespierre guillotine OR guillotined "face OR
facing upward OR up"
Google Web Search: robespierre guillotine OR guillotined legend