I was watching Derren brown's documentary the other day and it showed a clip where he payed for a few things with blank pieces of paper, but made the cashier think it was money. I was surprised that I haven't seen this clip before and wonder how real it is. I never really looked into the more mental/psychological side of magic (only one time a few years ago I read some stuff on hypnotism and went around trying to hypnotize people - I gave up quickly). So anyway I just wondered how 'real' it is. Is this a legitimate thing, was there pre-camera things or is it just set-up with actors, he did show a clip of him failing but this may be purposeful? More curious than anything, and if this is real then how often is this sort of psychology being used?