You show two packs of four blank cards each. You stick a blue dot on the top card of one pile and suddenly all these four cards have blue dots. You do the same with the red dot and the other pile. Then you exchange the top cards of these two piles. The remaining cards follow their leaders because the pack that had blue dots before has now the red dots and vice versa. When you take off a red dot and a blue dot from one card each, the remaining cards return to blank cards.
1st edition 2024, video 5:16.
