The Infinite Trick | Manfred Zöllner

They present four cards: three of the same, “the inseparables” and another, “the troublemaker”.
> And then a switch of places begins that is both amusing and inscrutable. One of the "Lovebirds" cards goes into the lapel pocket, but immediately it swaps places with "the troublemaker" and finds itself with the other identical cards.

This game is repeated and repeated...
... as long as you and your audience want it!