This morning in Greek class, she was there early, writing up some tables and forms to be used later in today's lesson, as she always does. In the corner of the whiteboard, though, was the following sentence: "Correction to ridiculous mistake: the propenultimate syllable can be stressed in Latin (e.g. obLIvio, CIcero)." And in smaller print "it is the ultimate syllable that's never stressed".
She must have realized her mistake while making it, or shortly thereafter, or some time after class. The point is that although she knows we all have enough Latin to recognize it for a slip of the tongue and not be confused by it, she felt responsible for uttering nonsense in class, and chose to make explicit her recognition of that mistake.
I admire this behavior with all my heart. This is good teaching ethics, in my book.