2. The nails are pink, shiny, moderate in thickness, moderate in hardness, not easy to break and smooth in surface. A healthy circle (half-moon at the bottom of the nail) accounts for one-fifth of the length of the nail (preferably five nails) as a sign of health. If the color is light yellow, cyan, black, dull, too thick or too thin, too soft or too hard, easy to break, rough and dull surface with concave grooves, vertical stripes, white spots and abnormal proportion of healthy circles, it is a sign of poor physical fitness.