That keel scatters the light differently than do the flat portions of the scale. Smooth Scales have a smooth surface that reflects the light. If you are not sure it has smooth scales, but your snake has a shiny, glossy or irridescent color pattern, chances are it has smooth scales. Keeled Scales usually have a dull, no-gloss surface. If you are not sure it has keeled scales, but your snake is not shiny and its color pattern is dusty, drab or dull, chances are it has keeled scales.
Some snakes have smooth scales on their back and keeled scales on another part of their body .
For example, the striped crayfish snake, Regina alleni , is smooth-scaled and very glossy. However, on the top of its tail and around the anal region it has keeled scales. Do not worry about these exceptions. In the Layman's Key to the Snakes of Florida you only have to decide whether the scales are smooth or keeled based on what you see on the snake's back.