[Cryptography] Crypto in stage magic

[John Levine]

A nephew who does stage magic for fun told me that he's working on
"mentalist" tricks.  In one classic, the magician is blindfolded on
stage, and his assistant moves through the audience asking people to
give him items that he holds up, and the magician guesses what they
are.  The assistant might say 

 "I have an item from a lady here"
 "Hmmn, seems quite personal."
 "I couldn't say"
 "I'm thinking it's a picture"
 "Is that right?"
 (woman) "Yes!"
 "Can you tell us any more?"
  ...
 "I'm seeing the lady's mother." (applause..)

This trick goes back at least to the 1800s, so there's no radio or
other technical cheat, the magician really is blindfolded, and the
audience members are not shills.

My nephew, who knows me pretty well, said, you can probably figure out
how this works.  Aha, it's steganography.  The magician and the
assistant have a code hidden in the words and timing and tone of the
innocuous back and forth.  Nephew says they can be very complex, items
can be split over multiple back and forth comments.  Some magicians
even did it with no words at all, using timing and sounds of
footsteps.

A little googlage found nothing on this trick.  But it must be well
known to someone here.

R's,
John