I'm taking a couple of graduate level classes this term, one in the History of Central Asia, and another in Stellar Dynamics and Hydrodynamics. I'm taking the history class with another old guy, a retired Archaeology prof that I've taken a couple of other classes with. The history students are friendly but rather reticent when it comes to asking questions, and as a result the two old guys without enough sense to keep their mouths shut wind up with an excessive share of comments and questions, and as a result the profs sometime shush us to get the "real graduate students" to participate more.
The Astronomy grad students, on the other hand, practically seem to have taken vows of silence. Dragging a conversational fragment out of them hard work. The Astro prof doesn't find it easy to get much out of them either. He was asking the class some rather elementary questions about tidal forces and nobody would answer except me, so he made me shut up and concentrated on the real students. After a little math, he asked them produce a Taylor Series expansion of 1/(1-r/R)^2. Now I'm sure that given a minute, everybody in the class could do that, but they froze under pressure. He was pretty unhappy, and said it was fifth grade algebra. I helpfully added that it was probably eighth grade algebra in the US (he is a Russian).
Of course I have to admit that your deservedly humble servant had a few moments of uncertainty about the sign of the linear term. (1 + 2(r/R) - ...) Fortunately he had already shut me up;-)