Tried-and-true audience favorite!
Show a two-sided giant domino card with a single spot on one side and four spots on the other.
Turn the domino card back to the first side- now there are three spots instead of one!
Turn it over again, and now there are six spots instead of four!
If that's not amazing enough, you pretend to "teach the secret" to the audience.
Just when they think they know how it's done- there are now eight spots on the card!
Very easy to do- if you can hold the card in your hands, you can do the trick!