I don't speak French. The "old folks" spoke French around us when we were kids and we knew they were talking about us kids. I guess they thought it better to not teach us as we would then know what they were saying.
I looked the phrase up and still didn't get the joke. It was the end of a long day.
Descartes was a fascinating dude - usaully, it is quoted as “Cogito, Ero Sum.” I think, therefore I am.
Before old Descartes came along, decriptions in Maths included phrases like, “In Triangulorem rectorum ...” , “In a right triangle...”
So Descartes took two rulers, and crossed them at right angles.
We now call this the “Cartesian coordinate system.”
Two rulers. Huh. Who knew.
But I put decartes before de horse.
;)