... is making the students go "wow." I got to do that twice yesterday and it was awesome. We were going over a rock identification lab, and when we got to pumice I walked over to a bucket of water and plunked a big 'ol rock in... and it floated. "Wow!" I also set a couple of moderately interesting rocks on the video overhead, turned off the light, and turned on a black light. They glowed. "Wow! Can you see if my rock will do that?"
I love demonstrations.