The ring of thread is used to create a channel through the bubble film. The frame is lifted from the tray of bubble solution so that a thin film spans across the frame. Students gently lay the ring of thread onto the bubble film. The students then take something dry, like the tip of a pencil, and pop the film inside the ring. To their amazement, the string pops into a perfect circle that floats across the film within the frame. This is used to illustrate channel proteins that create passageways across cellular membranes.