It's a day of revelations for my students. First they discovered, just like Moliere's M. Jourdain did, that they speak in prose. Then, I asked them (in Spanish, of course) if they spoke Castilian.
"No!" they answered in unison.
"Yes, you do," I said. "You just answered a question in Castilian."
"Get out of here!" exclaimed one of the students in English.
I'm not sure how I would translate that response into Castilian in a polite manner.