The cards are shuffled then riffled until the spectator stops you.
All the cards are lifted at that location and flipped face up to mark the spot.
You explain the routine is loaded with notifications.
The spectator notified you when to stop. The cards above the location were reversed to notify a selected card.
That card is set removed and aside.
The deck is notified when the card is removed and its twin is notified to reverse itself to notify us which card was selected.