Dan:
I’m guessing you might need some further convincing about the number guessing trick, and besides, I like talking about magic.
The way I would do the trick you described is with the “one ahead” gimmick, which is a pretty basic mentalist trick. I’ll give this one away, because you can find it in any magic book.
To do the trick requires an accomplice.
Let’s say you have five people. They are going to choose a secret number between 1 and 50 and you are going to astound them by guessing all their numbers.
So they don’t cheat you make them stand in a circle and write their numbers down, carefully fold them and put them in a hat with their initials on the outside.
The reason you need an accomplice in place is because you have to “know” what the first number is going to be.
Let’s say your accomplice has agreed to pick the number “25.”
You take the carefully folded paper out of the hat, squeeze it and look at your accomplice. You say "My superpowers say that your number is “25.”
He says “golly gee, that’s right!”
You open the paper to confirm it, and say “Yup, 25.”
Except, you didn’t pick the accomplice’s paper from the hat, you picked the next person’s in line! In open and plain sight, you now know what the next person’s number is.
You work on down the line, staying “one ahead” and as long as you don’t make it seem unnatural that you’re looking at the paper to confirm the number, nobody ever suspects it.
The amazingly inept Scylla uses this trick all the time.
The highly astute among you will realize that there is no reason you have to use numbers.
I like to do it at restaurants with my wife as the accomplice. My signal to her, is that I will look at the menu and say “the chicken looks good.” This signal means that she is supposed to order as her entree the item below whatever item I have named (or above) if it’s the last in sequence.
A few minutes later, I then make a challenge. I tell the people at the table that I love them dearly, and that I know them better than they know themselves. To prove it, I propose to guess what they will order as entrees.
They will say “Oh no Scylla, you couldn’t possibly do that.”
If I am feeling evil I say “I will put my money where my mouth is. If I guess everybody correctly you must all split the cost of my wife and I’s meal. If I guess even one incorrectly than all your dinners are on me. Isn’t that fair odds?”
At this moment, they will decide that I am a sucker and take the bait.
Now, there is a moral issue at stake here. I am stealing a free meal. If they are good sports about it when they lose, I tell them it was really just a dirty little magic trick and they really don’t owe me a dinner.
If they still want to buy my dinner, I let them in on the secret so they can earn back a free dinner.
There are all kinds of other methods, but I suspect blaine was using the “one ahead.”
It is very effective with just a little practice. Unlike most magic tricks this one works better the more skeptical the group is. You make a big deal about keeping everything honest by writing things down secretly and folding them up, and putting them in a hat.
Now you too, can earn a free dinner by preying on your friends!