Blackmail by Docc Hilford

Here’s the FIRST effect...
Show a single, plain coin envelope.
Ask a subject to get his wallet and take out a dollar bill.
He folds it (portrait inside) and drops it into the empty coin envelope.
You don’t touch the bill.
The envelope is closed.
The subject holds the closed envelope - while your hands are EMPTY!
IMMEDIATELY, you reveal the serial number!
No messing around or handling.
HE PUTS THE FOLDED BILL IN THE ENVELOPE and HE HOLDS IT.
The entire serial number is openly recorded on the envelope.
It’s spoken aloud so everyone hears the revelation.
After, the subject opens the envelope, looks at the bill’s serial number,
AND THEY MATCH!
Now the spectator can keep everything.
Look at this...
 
The same single envelope that the subject drops his dollar into, is the same envelope on which you write the serial number.
YOU NEVER TOUCH THE DOLLAR BILL!
Not before it goes into the coin envelope...
Not after the trick is over, to check the number.
YOU NEVER TOUCH IT!
The envelope doesn’t leave the audience’s sight.
THE SUBJECT KEEPS THE ENVELOPE AND HIS DOLLAR!
He can examine everything - there’s nothing to discover... EVER!
Also...