How do magicians touch cards and guess points?

The performer took out a deck of playing cards and dispersed in public. And repeatedly showed it to the audience, indicating that this deck of playing cards is the same as ordinary playing cards.

At the beginning of the performance, the performer asked an audience to randomly draw a card from the cards and handed it to him on the back of the signboard. He only touched it up and down for a while, thought for a while, and then smiled and said, "The color is red, and 1, 2,3 ... is a square 6." Card point is right. Then everyone took turns to draw cards for the performer to guess, and he guessed right.

But magic is always fake. It turned out that the performer had a new thumbtack between the index finger and middle finger of his right hand. Through the reflection of the thumbtack, you can clearly see the points on the card (in fact, it is enough to take a picture of the points on the side of the card). When touching cards, the performer's movements are free and vivid. Even if he had seen the card points clearly, he didn't say them immediately, but repeatedly touched them up and down, left and right, trying his best to convince the audience of his "guessing points by touching cards" through these fake actions.