In this mind reading trick, Criss Angel astounds Oprah Winfrey by revealing the number she is thinking of. She first selects a number between 1 and 100, writes it on a pad and shows it to the audience. By reading her body language, Criss succeeds to find out what number she is thinking of.
While reading body language is a very useful technique and sometimes really is used in mentalism, this trick has a much simpler explanation. There is a good reason why Oprah had to show her number to everybody except Criss. He probably had an assistant somewhere in the audience, ready to spot the number and secretly communicate it to Criss. You may have noticed that over two minutes pass from when Criss opens his eyes to when he reveals the number. More than enough time for his assistant to signal him the correct number. There are many ways in which this could be done: hand gestures, body positions, facial expressions … You don’t need a lot of imagination think of a way of doing it without attracting attention. After all, we’re only talking about two numbers.