The key to solving this puzzle lies in understanding the setting of the problem. This puzzle assumes that the opponent (that is, "psychic detective" or "haunters") has extraordinary reasoning and/or perception ability, and can know the cards you remember without directly seeing or touching your cards.
To solve this puzzle, the first thing to be clear is that you didn't tell the other party that you had cards in your hand or show them your cards. So, how does the other party know that you have cards in your hand?
The key point is that in the setting of this question, the other party is a "psychic detective". This means that the other person may have the ability to read minds. In this case, the other party may know that you have a card by some means (such as micro-expression analysis, verbal suggestion, etc.). ).
However, if the opponent is just an ordinary person and you don't think he can know your cards in any physical or logical way, then the answer to this question is more complicated. In this case, the answer to this question may be obtained by the other party through some logical reasoning. For example, he may infer that you have cards in your hand by inferring your nonverbal behavior, such as the micro-movements and gestures of your eyes when you look at cards.
It should be noted that the answer to this question depends on how you set the conditions of the question. If you think that the other person is just an ordinary person and has no superior reasoning and/or perception ability, then the answer to this question may be obtained by the other person through some logical reasoning. If you think the other person is a "psychic detective" with extraordinary reasoning and/or perception ability, then the answer to this question may be that the other person learned it through his mind-reading ability.