|How can you make noise by running your finger (if it's wet) along the rim of a glass?
If you run your damp finger lightly along the rim of a crystal glass, it should begin vibrating. This trick involves a resonant transfer of energy in which your finger rhythmically pushes on the glass to make it vibrate more and more strongly. It takes a delicate touch. If you press to hard, you will prevent the glass from vibrating. If you press too lightly, you won't give it any energy. Your finger must stick and slip alternately, just as a bow does while sliding across a violin string.