I encourage my students to ask questions. Students questioning are students thinking. When I am questioned I am forced to look at what I am doing through the questioner's eyes and this allows me to view my teachings from many different perspectives. Sometimes the questions are deep and moving, coming from long thoughtful introspection; sometimes they're just plain silly. Each time a student poses a question I learn something about her/him. This is invaluable to me as an instructor. Equally important, my students can see me in the light of their own uncertainties. They see that I don't have all the answers; that some questions must be answered from the inside out.
I also encourage discussion during class demos. The exchange of ideas and insights is interesting and helps to foster the strong sense of community at our dojo.