Feet can tell you a lot about your body. Calluses, for instance, can tell you where there is stress in the body. Callus on the back of the heel tells you that you are pitching your weight to the lower back. Callus on the side of the big toe is a stress cue that could be pointing to stress at the base of the skull. Callus on the ball of the foot directly below the little toe could be pointing to shoulder pain.
Curled toes tell you a lot as well. They usually indicate hidden pain in the ball of the foot. The toes try to curl to protect the area and give you a little lift off the ground. It does not work very well but often points to tension in the upper back and chest.
These are visual stress cues which are the easiest to pick out. But there are also touch and what we call "press and assess". The later stress cue is fun in classes for picking out tailbone injuries. Bubbles will appear on the side of the foot when you press the heel. Always a crowd pleaser.
I will cover more stress cues in this blog but if you want more information on this The Complete Guide to Foot Reflexology and MyReflexologist Says Feet Don't Lie cover this subject extensively.