A couple yudansha where I train are very good at non-verbal correction. I do the technique, then they do the technique slowly with great emphasis and control on one part. Then I try, and the next time either some smaller nuance gets emphasized or whatever.
I've always had my doubts about this particular approach. There are a lot of reasons to keep the talking down, but one of the chief ones for me is to keep me focused on my own learning and to guard against the tendency to cheat myself and others by focusing on their learning instead of mine. I feel like what you describe, Deb, runs the risk of crossing that line.
On the other hand, often times a mistake made by someone I'm training with will cause me to think about my own behavior in that particular aspect of the technique. Sometimes, that will bring my focus to that aspect, highlighting things both for me and my partner.