The disappearance trick can only fool monkeys with opposite thumbs. Reported by Cambridge University.
As part of this trick, the spectator has the illusion that the object coming out of his palm is being picked up with the other hand, but in reality it simply falls and is hidden behind the palm of the same hand. Despite its simplicity, for a person this illusion seems convincing, especially for children.
Now scientists have realized that for this trick to work, the anatomy of the “victim” must resemble the anatomy of the magician. In particular, monkeys without opposing thumbs were immune to this illusion. This was found during experiments where pieces of food were substituted for coins for monkeys and given as a reward, but only if the animals guessed the correct hand. The experiment was conducted with 24 animals: eight capuchins tried to trick them with peanuts, eight squirrel monkeys with dried mealworms, and eight monkeys with candy. Capuchins are renowned for their agility and in the wild they use stone tools to crack nuts. They can wiggle each finger and have opposing thumbs for a secure grip. This trick fooled them 81% of the time.
Squirrel monkeys have much less dexterous hands, but their thumbs are partially opposite. Their focus was misleading 93% of the time, suggesting that anatomy can only partially match for the trick’s success. Monkeys, on the other hand, whose fingers are perfectly stacked and adapted only for climbing branches, had no problem identifying the “correct” hand – they only managed to cheat in 6% of cases. This matches the selection of intelligent animals with no arms, such as ravens.
According to scientists, this may be because when we observe another person’s action, the same neural connections are activated in our brains as if we had made them ourselves. So the animal can “lose” someone else’s movement in its head and understand it better.