some laughter in class

"Any questions?", Prof. Facchini asked.
"Yes, why does the point not shift along the RS curve, but shifts to RS一丿儿", answered one student.

there was a sudden burst of laughter in the classroom, lasted like one or two minutes. It's so funny when he said it, I almost jumped from the chair! But you could see clearly the stunned expression on the faces of foreign students and Hong Kong students. They starred at each other, totally had no idea what happened.

Well, here's the funny point. When he said RS一丿儿, he actually meant RS' (which is pronounced RS prime in English). But he didn't know how to express the superscript, instinctively used the Chinese version "一丿儿".
so basically: ' = 一丿儿