We're thirty minutes into this birthday party, nobody's served food yet, and the other parents are starting to look pretty tasty when you show up: the entertainment. This family has hired a stage magician to entertain their third-grader and his friends. So there you are, and there I am. And then you started your performance, and it was excellent. Except...
I saw that card fall out of your sleeve, land on the floor, and then jump back in a moment later. It would have been a grand bit of stagecraft, but nobody saw it except me. Or the bit where you held out a coin and then pretended to pull it out of the birthday boy's ear. Nobody but me saw you hold it out. They all thought your hand was empty. And then the birds that came out of your hat? The ones that nobody had to chase out of the house later? That was the one that really gave it away.
I gave myself away too though, didn't I? I looked at something I shouldn't have been able to see once or twice too often. And then you started looking at me. And then the show was over, and you left before I could catch up with you.
Well... I guess by now you've figured out what I am. I want you to know that it's not what it seems. If you want to know more, look me up. You're a lousy magician, but you're a very impressive sorcerer.