Show the audience a bank note.
Fold it in half as shown.
And then again in half.
You should have this.
And now unfold the bank note in reverse. Nothing about it has changed.
Repeat, folding up the bank note as before. And unfold it. Now the bank note is upside-down, although everyone saw that you didn’t turn it over.
The secret is that the second time around, you unfolded the bank note in a slightly different way.
Unfold it backward, not forward.
And at the end, unfold it upward as before.
There is, in fact, another way to unfold the bank note. It’s worth memorizing. At first, unfold it like the first time.
And only at the second step unfold it backward.
And then, as usual, unfold upward. Unfold the bank note quickly, and no one will notice that you did something different at the second step.