Magic Tricks

I bought this because my wife is a nurse and I thought she might be able to mystify her students with it. However, just before I hit the "Pay" button, a possible solution to this trick came to mind. I thought, "There's no way it could be that easy." I was wrong; it is just that simple. There are only a couple of variables here, so if you aren't controlling one, it must be the other.
Now for those of you who are mentalists, the author includes a number of ways this trick can be included in a routine and that may be well worth the price of admission. I am not a big fan of mental magic and will likely never employ those procedures.