"A sur coq" - probably came to pass on a Monday morning.
The engraver started on the privy mark, a rooster, or coq, but he put it on the wrong side.
After realizing his error, he puts the rooster where it should be, and attempts to conceal the first rooster by engraving the mintmark, "A", for Paris, over the top.
Which has the effect, of course, the the "A" has a head and a tail.
Gadoury calls this variety "A regrave sur le coq"
This link takes you to an article, en Francais, with several good pics, scroll down to page 9 -
http://www.numishop.eu/bn/bn041.pdfPeter in Oz