Detective aces

Take out the 4 aces from the deck and place them face-up on the table.

Deal 4 piles, and when the spectator says "stop", put an ace face-up where you were. Continue dealing cards on the other 3 piles. Repeat this until you placed all 4 aces.

Next, put the deck all together and cut it. If you cut on an ace, cut again.

Finally, spread the deck, take the 4 aces and the cards just above them : they are the 4 jacks.