This trick involves a rubber band that gets wrapped around two fingers. By doing nothing more than lifting your fingers, the rubber band appears to instantly transport itself to the other two fingers on your hand. It sounds simple, but I'm always amazed how confused people get when I show off this trick.
Step 1: One Rubber Band
Step 2: The Secret...
Make sure the rubber band placed around your two fingers in the previous step is below your knuckles. Use your other hand to quickly grab the rubber band from the palm side. Bend your four fingers and put them through the rubber band and let the rubber band snap back in place.
So at this point, the rubber band should appear to be around two fingers on the back side of your hand and around four fingers on the palm side.
Step 3: Make the Jump
Once you have the basic move down, this can be dressed up as seen in the attached animation.