Vincent at Ensis Sub Caelo has published an English translation of an excerpt Jean-Joseph Renaud’s Traité d’Escrime Moderne (1928) where Renaud discuss the secret thrust, or botte secrète.

Nevers’ attack strikes the villain in the finale of Le Bossu.
“A fencer smiles when he hears of
secret attacks. He knows, or thinks he knows, all the resources of fencing and does not really admit he could be surprised by an unknown trick. Oh, he does not think himself untouchable…”
Follow this link to read all of Victor’s translation on Ensis Sub Caelo.