I know you guys have probably seen this before, the "think of a number from one to ten, is it 7?" thing mystery does.
As you all know, it doesn't hit all the time, and that's why a lot of people don't do it. "What if she thinks of 3 or whatever?"
Here's the handling that I use to open a lot of my professional close up sets. The nice thing is, you're never actually wrong, regardless of the number thought of, which lets you be a LOT more confident.
"Think of a number from one to ten, quickly, and try to go with your first impression".
as I say this, I trace a 7 in the air absentmindedly with my finger.
"You're not thinking of a seven are you?" (this wonderful statement can go two ways...)
She says, "Oh my god! how did you know?"
to which you reply "It's an old trick I learned in psychology class, I don't know if you noticed, but I traced a seven in the air with my finger as I was talking to you. It's funny how things like that have so much influence over us!"
---OR----
She says, "Nope"
To which you reply, "Good! everyone seems to think of seven for some reason, what number did you think of?"
Her, "5"
You, "That's really interesting, they say that people that pick 5 are very individualistic, and although they are very social, they tend to have a private side very few people get to see. I bet people tend to lean on you a lot, socially. This can be annoying sometimes, but in the grand scheme of things, it makes you a stronger person. It's kind of funny how little decisions like that can reveal so much about what's going on inside a person's head. it's FASCINATING to me."
As you can see, the "trick" goes two different ways, one, you "psychically" force her to think of the number seven, the other, you are giving her a personality reading based on the number she thought of. Both of these eventualities are chick CRACK, and make you look all mysterious.
Oh, and by the way, I give that same reading regardless of what number she chooses :-) Notice how the term "lean on you socially" can mean about a bajillion different things.
Either way, you can't fail, so I hope you try it out!