One day a young man was visiting the fair, over to one side was a small tent, with a sign that said "For 50 dollars I'll teach you to be a mind reader!  Apply within."

So the young man thought that he'd give it a go, and went inside.  Behind a small table inside was an old man, who looked up when the young man entered and says, "Ah, you must be here for the mind reading lessons."

"Well, yes" the young man said.

"Well, follow me, and I'll give you your first lesson." Then the old man goes out the back of the tent and walks over to a hose, which he picks up one end of.  "Here, hold this hose."

"Why?" said the young man.

"It's part of the lesson," replies the old man, "Now, look in the end and tell me what you see."

So the young man looks into the end of the hose, and only sees darkness.  "I don't see anything," he tells the old man.

Just then the old man turns on a tap, and the hose shoots water into the young mans face, "I had a feeling you'd do something like that!" the young man shouts at the old man.

"You are now a mind reader!" the old man replies, "That'll be 50 dollars."

(BTW, the real secret is here)