Predict a book among millions

Effect

The mentalist asks a mobile phone to a spectator, announces that it is going to make a search on internet and once is done, leave the phone on the table
asks the spectator if he had to find something on internet, that would look for and where you do it? The spectator names such as Amazon and seeks harry potter book...

Under these conditions, the mentalist ask the spectator to take his mobile phone and look which was the search done

Under such conditions, the spectator will find a search done in the Amazon page with the book you just named.
spectator could have named any library any book even any author, but nevertheless, the prediction will always be 100% correct.