Hi Simon,
I think I do know how it works!
(Ok, to be more precise, I know how
I could exactly reproduce the effect; you never
know the actual method used unless you are told it. Hmmm sounds like a Philosophy Of Knowledge lecture
Anyway...
As you say, you could use a sticky card but it starts to get awkward. Also ideally you want the signed card to be examinable at the end - so that raises questions about
when in the method you use sticky-cards.
Another idea is if your instructions were printed on a blank-faced card with a
normal back. Problem then is that the method becomes more obvious. Unless you do what you do - & turn it into a 'normal' card to wallet routine. And if could show you still had your instructions, this would be a nice convincer.
Anyway, my question was really less about the method & more about the effect. Since it is SO impossible that they signed the card you were holding all along, there 'must be' an alternative explanation - but will laymen figure it out??? I guess this is a general question about whether an effect can be
too strong. It seems like maybe you felt it was - because of the change you have made to the handling. I am interested in what your thought process was?
Regards,
N