Put your right thumb in the middle of your right palm and tuck your hand in your right arm pit with your fingers pointing up. Keeping your hand tucked, take the thumb out of your palm and then try to put it back. It makes your wrist hurt. How come?
Bite down hard as you can stand with your incisors on the middle of the fingernails of both pinkie fingers for about five seconds. Take the pinkies from your mouth, interlock them in front of you and pull apart. It makes your fingernails hurt in a new way. How come?
Grab the index and middle finger of your left hand and squeeze with all your might for at least thirty seconds. (All your might!) Then relax and open your right hand as slowly as you can. You open in little jerks. How come?