Share this amazing trick with your child, and you'll have her feeling like the strongest kid on earth.
Help her select a piece of yarn, string, or lightweight cotton that's at least 3 feet long. Loosely wrap one end around her left forefinger a few times, leaving a loop in her palm and letting the rest of the string hang down behind her hand, as shown.
Help her bring the hanging string up and through the loop in her palm.
Wrap the remaining length of string around her right hand several times.
Now have her clench both hands into fists, grasping the string tightly, then quickly yank apart her hands.
She should find that the string breaks easily. Here's why: passing the string through the loop in her palm in step 2 focuses the force of her pull on that small area, right where the string intersects itself, making the string cut through itself.