The Power in My Little Finger

Have your volunteer sit in a chair.
Ask him to keep his head a bit back and his chin up.
Now start your patter about the power you have in your finger.
Place your finger on the volunteer's forehead.
Ask him to stand up.
He won't be able to stand up with your finger in place.

What's Going On
With the head back the volunteer can't stand up without pulling his head forward. But you have your finger in the way so he can't stand up period.

How I Would Use This

This trick can be developed using the Power of Patter; that is the stuff you say while doing the trick.

One way to enhance the trick is to talk about the might and power of the smallest things, example your finger. Show your finger. Then set up the whole trick and show how powerful it can be applied in the right way.

Be creative, there are all kinds of applications you can make for such an open-ended activity.