This is an easy one, but it will baffle people who don’t know how to do it.
All you need is:
1. A piece of rope 3 or 4 feet long.
Step 1: Hold the rope as in Figure 1, and give your friends a chance to try to tie a knot in the rope without at any time letting go of either end. When they give up, take back the rope and lay it down on a table.
Step 2: Cross your arms before you pick up the rope!. Pick it up one end at a time to make it easier to grasp.
Step 3: When you uncross your arms, a knot will appear in the middle of the rope, without your at any time releasing either end!