The magician shows a piece of cardboard that resembles a cheese wedge: “This is not a piece of cheese, it is the cardboard cut-out of a piece of cheese”.
“It is a piece of Dutch cheese. You can recognise this as the holes run horizontally” (top image). The magician shows the card on both sides.
“What is the difference between Dutch and Swiss cheese?”, she asks the audience.
She places the card in her fist, indicates the moment of magic, and reveals the card again.
“Dutch cheese has horizontal holes, and Swiss cheese has vertical holes” (bottom image). The magician displays the card on both sides to show that the holes have moved from the side to the top of the cheese.1
Ambiguous Depth Illusion
The principle behind this magical oddity is the ambiguous depth illusion. This illusion occurs because our mind interprets lines on a two-dimensional surface as a three-dimensional object.
When interpreting lines as three-dimensional objects, the mind is sometimes confused. The brain interprets some drawings in multiple ways. Famous examples such as the Necker Cube and the Schroeder Stairs, shown below, demonstrate this illusion.
As you stare at these two images, you notice your mind constantly changing its interpretation between the two possibilities.
For the Necker cube, either the left or right square appears to be at the front. The Schrödinger stairs can be viewed as either sitting on the ground or hanging from the ceiling.
Ambiguous Depth Illusion in Magic
Other magic tricks based on the Ambiguous Depth Illusion are Parabox by Jerry Andrus and Escheresque by Daryl. Another famous trick that uses an optical illusion is the boomerang trick.
Instructions and Construction Template
You can easily make the props and perform this trick based on the images on this page. If you are interested in knowing more about this optical illusion trick, then please purchase the instructions with the construction template.
This routine is based on an idea described by Bob Hill from his 1994 booklet Illusions that Reveal the Truth (used with permission). ↩