The way this works is that if a feeder or feedee reads this page, they will know how this exchange will go. If the exchange goes exactly like this, you know they are a feeder or feedee, there is simply no way that this exchange could randomly go exactly like this.
We have person A and person B, A is the initiator, that wants to know.
A: "Do you know what my favorite movie is?"
B. "I don't know, which one is it?"
A: "Willy Wonka and the Chocolate Factory"
B: "Ahh, yes, I love that one too" (or any other response, this is basically just to set up what is coming)
A: "Do you know which one is my favorite character in that movie?"
Now here it comes. This is a trick question, since many people have seen the new version of Willy Wonka and will answer very predictably the wrong thing.
B: "Oh, I know which character that must be. Violet!"
A: "Yes, I it is Violet!"
Now, what would a non-feeding person probably say?
B: "Oh oh, yes, I know. JOHNNY DEPP!!! I love him in that movie!!!"
So I laid that trap deliberately, EVERYBODY loves Johnny Depp, no matter in which movie he plays. Now if you are a feeder and feedee like me, you of course prefer Violet because she pumps up and grows, which is so hot.
To make the thing really fool proof, another exchange:
A: "Do you know what I wish they should do with her?"
B: "Oh, yeah, they should do a movie just about her!"
A: "Oh yes, you can read minds, can you?"
At which point it is safe to breach the question:
A: "Are you a feeder or feedee?"
B: "I 'm a feedee!"
So the cool thing about this is: you can try this out on somebody and it is totally innocuous. If the other person is not a feeder or feedee, they will just answer differently. There is no way that they would accidentally get all the things right. So this gives you the possibility to scout for feeders and feedees without the danger of getting yourself into hot water of exposing yourself as being into feeding, while the other person is not.
You only expose if the other person is, they recognize that you are, because they know the "secret handshake"
Now the really nice thing about this is, that it is not even perceived as a secret handshake by the non-initiated.