What is the principle of bird fortune telling?

Birthday counting and decryption of birds.

The reporter saw at the scene that the stall owner of the "Lingniao" fortune-telling prepared several birthday cards marked with the date of the whole year in advance, and plastic sheets also marked with the date of the whole year were placed on the ground. When telling fortune, the stall owner asked the fortune teller to pick out a card indicating his birthday (there are other dates on this card). Needless to say, as long as you put it in a small box marked with this date (there are other dates in the box), and then let the bird peck or look at it, the stall owner can tell the person's birthday. People who don't think carefully are particularly surprised and believe that this method works.

In fact, there is only one date on that card that can correspond to the corresponding plastic box, and that is the fortune teller's birthday. In fact, the fortune teller himself told the fortune teller his birthday through action. The fate of the so-called fortune teller on the small paper bag that the bird took out was written by the fortune teller in advance. Although not all of them correspond to each other one by one, on the one hand, I firmly believe that "Lingbirds can count as birthdays", on the other hand, most of the accompanying notes written by people are flattering and encouraging words that people are willing to listen to, which seems to correspond to their own experiences.