xx Marvin teaches the Colour-Blind Blocks xx

Three coloured blocks are displayed, then a spectator hides one inside the mysterious bag. Even though you never look inside the bag, you always know which colour block is hidden.

Secret: Each block has a slightly different shape. Although you cannot see through the bag, you will be able to feel the shape of whichever block is in there.

Have a close look at the three blocks. You will notice that, although they look the same, the edges are all subtly different.

The first block has two square edges. The second block has both edges rounded. The final block has one square edge and one round edge. Because of this, if you pick up the bag between your fingers and thumb (so that you can feel the long edges of the block inside), you will instantly know the colour of the block!

During the performance, you should hand the blocks and bag out for examination. Then ask a spectator to place one of the blocks inside the bag while your back is turned.

Once this has been done, ask the spectator to hide the other two blocks, so that you will have no clue which block is inside the bag.

You can now turn around and pretend to read the spectator’s mind to discover the colour of the block inside the bag. As you do this, you should casually pick up the bag between your thumb and fingers and move it away from you (as if the bag were not important to your mind reading powers).

Once you have secretly felt the edges of the block inside the bag, you can dramatically reveal the colour of the hidden block. As long as you do not appear to pay any attention to the bag as you move it, no one will guess that you are secretly feeling the shape of the block.