The theremin was the most confusing exhibit I got to see at my visit to the Exploratorium today. I couldn't figure out how you could make music using it without touching the theremin itself!
The most interesting exhibit I saw today was the glow discharge tube! I thought it was interesting because I have always wondered how auroras worked and how they made such fascinating displays of light in the sky. The glow discharge tube explained just that.
The listening vessels deserve an honorable mention! I grasped the concept of how they worked, but just being able to have a conversation with someone all the way across the room was captivating, engaging, and fun.