You walk out on stage and place a large card on a chair or

easel facing the audience. The card has three shapes drawn

on it; a square, a triangle and a circle.

You choose an audience member and ask him to stand. You

explain that when people are asked to think of a simple

shape, these are the three commonest designs chosen. You

ask him to choose one of the shapes, in this case he

chooses the square.

You then ask him to reach under his chair where he'll find an

envelope stuck underneath. Ask him to remove the envelope

and as he does so, explain that earlier on you made a

prediction as to which shape he would choose and stuck it

under his chair.

When he opens the envelope, there is a postcard inside that

reads 'You will choose the square'.

This is a nice opening effect and usually works very effectively.

Make a large card with the three shapes drawn on it as described

above. On the back write, “You will choose the triangle”. Write “You

will choose the square” on a postcard and seal it in an envelope.

Before the show, stick the envelope underneath a chair in the

auditorium.

To perform the effect, simply reveal the appropriate prediction either

by asking the spectator to remove the card from under their chair or

by asking him to come on stage and turning the card around to

reveal the prediction.

If he chooses the circle, then your prediction fails but all is not lost.

State that most people choose either the square or the triangle and

because he has not done so, that makes him an interesting choice

to participate with an experiment.

Note that you don't mention anything about the prediction until the

spectator has named their choice.

If your prediction is right, then great! If not, disappointing but you've

not yet mentioned your prediction so no one is the wiser. Just get

the person up on stage to assist with a sure fire effect whether the

prediction works or not.