You show two tall plastic cups. The cups are tipped, and 4 coins come out of each cup. The coins are dropped back into the cups, and the magic begins!
You pretend to remove a coin "invisibly" from one cup, and toss it "invisibly" into the second cup. When the cups are tipped, 3 coins emerge from the first cup, and five coins from the other! The coin really did travel invisibly from one cup to the other!
The coins are replaced and this is repeated, with one coin removed from one cup and re-appearing in the other, until all 8 Coins have gathered in the same cup!
Best of all, once you know the basic principle, you can modify this routine and use eight coins, six coins or four.