What you do is you ask a person to hold out their arms perpendicular to their sides and attempt to hold them up (As if they're forming a T shape with their body and arms). You grab their arms and attempt to push them down for a moment.
Then, hold out your arm in front of you, turn your hand side ways as if you were about to chop something, and wave your hand downward directly in front of their face at a reasonable speed for them to follow with their eyes but not terribly slow. It should look like a slow chop through the air in front of their face and should only last from the top of their had down to their jaw or neck.
Finally, ask them to hold their arms out again and attempt to push their arms down once more with the same amount of force. It should now be harder for them to keep their arms held up.
Congratulations, you're a Jedi maybe.
Figured this out today in Programming instead of the project we're supposed to be working on. Anyone else have a neat little trick involving the brain that they wish to share?