One of my students was absent for a couple days, and then came back. And suddenly I realized how much I'd enjoyed the class discussion in his/her absence.
I would give a lot if in one of my lower level classes, one student would actually raise his/her hand and respond to what was said before by another student. Sometimes there's a relationship between what the second student says and what was said, but the second student almost never seems to recognize that.
(Okay, once in a while, but not nearly as often as I'd like.)
One can say the same thing for some department meeting discussions, alas.