This is a good idea, you want to do a trick that has been taught over and over again on countless TV shows, in other words, a trick that almost everyone knows. You wouldn't demonstrate how to do STS or Greed, to name two.
The torn & restored napkin trick is good, and will probably win you points from your teacher.
When I was in college, we had to "sell" something. I sold a "special" dollar bill: It was printed upside down (joke), it floats, (IT), it can't be punctured, (misled), automatically restores itself if seperated, (torn & restored), and vanishes for safe keeping.
I only had a limited amount, and the bills could be purchased for a mere five dollars.
I sold four.