The magician puts a packet of cards on the table. He says to the spectator, “Let’s play a game of imagination. Imagine that these are the four queens.” He pantomimes plucking a card with each hand from the packet. “Imagine that I have removed two of the queens. Do you think they are the black ones or the red ones?”
 
The spectator says, for example, red. “That’s amazing! You’re correct again!” He turns one of these queens face-up. He pantomimes turning one card over, then putting the imaginary cards back into the packet. He says, “Which red queen do you think I turned over, the heart or the diamond?” The spectator says, for example, diamond. “That’s amazing… you’re correct again!”
 
Of course, it’s really true then the queen of diamonds must be reversed in the packet. Let’s see.” He spreads the cards. One is face-up. It is the queen of diamonds.
 
“I want to be sure that you understand that this magic was accomplished by imagination, not sleight-of-hand. Therefore, I used a queen of diamonds with a different back color.” He turns over the queen of diamonds, showing that it has a contrasting back color.
 
“Also, because I knew you would pick the queen of diamonds, it was not necessary to use any printing on the faces of the other cards.” He turns over the three face-down cards, revealing that their faces are blank.
 
In the 1950’s magicians began inventing methods for doing the Brainwave effect with a small packet of cards. The basic plot is that a set of cards is shown, for example the four queens. A spectator is asked to name any suit. When the packet is spread, the queen of the named suit is found face-up; the other cards are face-down.
 
There have been versions published by Dai Vernon, S. Leo Horowitz, Ed Marlo, myself and many others. Some of these versions had the extra Paul Fox effect, that the reversed card also had a different colored back than the other cards. In 1978 Karl Fulves published a suggested extra effect, that the face-down cards had different faces (for example, all aces, or jokers, or blanks). I have published several versions of this. This is the most recent one.