Both cards can be examined at the commencement of the effect.
The performer explains that often squares change places with circles and vice-versa, and offers to prove this point. The card with the circular hole is placed inside the performer’s trouser or jacket pocket. After a snap of the fingers. It is seen that both cards have magically changed places. Again, the cards can be handed out for examination.
Complete with special cards and instructions. A novel packet effect, at a very affordable price !