According to the Davenport instructions, this amazing trick was evolved by Dai Vernon in 1930. The effect was that a mentally chosen card was found to be the only one turned over in the pack of cards. In 1932 Paul Fox told Dai Vernon of a variation, in which the mentally chosen card is not only turned over in the pack, but it also has a different coloured back to the rest of the pack. This is the Brain Wave trick. Complete with instructions.