Simply put its a method to have one volunteer clearly and openly read the mind of someone else. A gentleman standing in the audience thinks of a word. The lady on stage is coached in how to decipher the man’s thought. She agrees that her choice is a free and fair one, that you have not at any time told her the answer. She starts to write on the pad in her hands. Your back is turned, yet you ask her at this last moment to ‘change her mind‘. The lady tears off the paper and starts to write a new thought. Again she confirms this was a choice she made just now, and you have genuinely never met before.