Triple Vision by David Regal

An ultra clean prediction of three cards. The prediction can be in an envelope from the start. It can be sent to a spectator a week ahead of time. The prediction can even be "open", left in full view before you begin. Magicians have come to David's Magic Castle show a second and third time to try and figure out how this trick is done. Interestingly, the predicted cards can easily be made to change with each performance, frying the minds of those witnessing the effect for a second time. A subtle use of a principle.