Technology has advanced remarkably during the last decade. Scientists can see the light from a single molecule. In addition, they can mechanically manipulate (for example, pull apart) a single molecule. Such experiments produce two types of output. They produce a sequence of little flashes of light with different colors or bending of a tiny spring when force is exerted on a molecule. One must decode such raw data to provide new and important information about how molecules work. We can learn how molecules move, change their shape, and interact with each other and with drugs.