Have your spectator choose a number between 0 and 9 and double it. If she chooses 4, it would then be 8.
Add 8 to the number after Step #1. If you end up with 8, it would be 8 x 2 = 16.
Divide the Step #2 number in half (16/2 = 8).
Subtract the original chosen number from the new number. If she chooses 4, you will subtract 4 from 8 and end up with 4.
Convert this number to a corresponding letter: A=1, B=2, C=3, D=4, E=5, F=6.
Have your spectator think of a country that begins with this letter.
Have the spectator think of an animal that begins with the SECOND letter of the chosen country.
Look at your spectator and say, "Oh, you know there are no elephants in Denmark!"
This works just about every time due to the quickness of the calculations and because everyone will always end up with 4, thereby choosing a country starting with D.