The first one is very simple. Liu Qian has two hands, a pen (pocket) and a piece of paper When the audience speaks the numbers, he can secretly write them down as long as his hands are clenched. There is nothing in the red envelope. All he has to do is open the red envelope and make the note look like it was taken out of it. The key point is the ring on Liu Qian's hand, which is not necessarily just an ornament, but also a mystery. )

The second magic trick:

But Liu Qian has written the corresponding patterns on the back of five pieces of paper in advance (for example, the front is round, the back is square, the front is square, and the back is+). The back is specially made of chemicals (it has two functions: one is to image on the back, and the other is to distinguish it by itself). Or Liu Qian uses special contact lenses.

Liu Qian, as long as you remember the correspondence between the front and the back, you can see which card Dong Qing chose from the back. All he has to do is put the corresponding one back on the top one and drop special ink (chemicals) for a certain period of time, so that a chemical reaction can take place and develop.