Kostya Kimlat appeared in episode 7 of season 2 of the TV show Penn & Teller: Fool Us. He performed a card trick with Penn and Teller as spectators.
Next, he asks Penn and Teller to select one card each. They can take any card from the deck, regardless if it's face-up or face-down.
Kostya then asks them to insert their cards back into the deck, anywhere they want. They can put it in facing up or down, it doesn't matter. After they have both inserted their cards back into the deck, Kostya puts the deck on the table, and says that the cards will start to move by themselves and all turn in the same direction.
He spreads the deck on the table and miraculously, all the cards are now turned face-up! All except of two. And it turns out that those two cards are exactly the two cards Penn and Teller selected from the deck!
See the video, then read the explanation below.
Why did Penn get so angry about this trick? There is actually a funny story behind it. You see, Penn and Teller performed an almost identical trick on TV just a few days before. They know exactly how it works. However, Kostya managed to do a variation of their trick that fooled them! They had no idea how he did it.
First thing you need to understand is that most of the trick is just misdirection. It doesn't really matter what Kostya is doing. He is just playing with Penn and Teller. All the shuffling doesn't really matter.
The key to this trick is at the very end, when Penn and Teller are returning their selected cards back into the deck. It seems that Kostya is just very innocently going through the cards, letting them put their cards anywhere they want. However, that's exactly when the real trick happens.
Kostya is actually separating cards into two piles as he goes through them. Into one pile, he puts all the cards that are turned face-down. Into the other pile, all the cards facing up. He does it so smoothly that you don't notice anything suspicious going on. In the end, he just merges the two piles into one deck and puts the deck on the table. Trick completed!
If you want to learn this technique or see how it looks in practice, here is a great video tutorial: