hardly any secrets in professional gambling. Those casinos are expert in reading human behavior, eye movement, fin gets moving, facial expressions. I think card counting is the number one reason people are 86’d.
I worked prisons for 28 years. I remember an old timer that could tell you from watching an inmate for 15 seconds, he’s up to something, he’s holding (has a shank) and so on.
I recently saw a young Asian girl who rifled thru a deck of cards, memorizing each one. Then after all the cards were dealt out to 4 or 5 other kids, she was able to name the card when any of the kids was told to turn over the top card in their pile.