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© Copyright 1997, Jim Loy
Clever Hans was an amazing horse who could do arithmetic. Someone would tell Hans an arithmetic problem, and the horse would pound out the answer with his front hoof. He was very accurate.
Actually, Hans could not do arithmetic, nor could he even understand the arithmetic problems that were given to him. But, he was smart. In some ways, he was smarter than his owner and the scientists who were fooled by his trick.
Someone would state a problem, like "What is five plus eight?" Hans would start counting. And he watched his owner closely. When he got to the right answer, he would get some unconscious clue from his owner (relief of tension, or raised eyebrows, or something), and stop counting. The only times that Hans missed the correct answers, was when his owner miscalculated or didn't understand the problem. And, Hans fooled a lot of respected scientists.
It would seem that Hans' owner was not in on the trick. Hans could even do his trick without his owner being present, as other people gave him similar unconscious clues.
People who test supposed psychics must be very careful to not give clues to the correct answers. So, double blind experiments (in which the testers do not know the correct answers) are the only kind that can be valid.
When a psychic (or astrologer, palm reader, or graphologist) amazes you by telling you all about yourself, you are giving them many blatant clues with your reactions to their guesses and questions. Some of them may not even be consciously aware that they are tailoring their guesses to your reactions. Their trick is called "cold reading," and it is a skill they learn by practice.
A friend of mine has a cat who can do arithmetic. I asked him what five minus five was. And he said nothing.
Addendum:
There is a book called Teaching Your Baby to Read. The idea is to hold up two flash cards with words on them, and ask your baby which of them has the word that you say. For example, hold up COW and MOTHER, and ask your baby which says "mother." And your baby learns to point to the card that says MOTHER. This greatly benefits baby (and his/her parents), and probably leads to a joy of reading. But, the baby is not reading. The baby is performing the Clever Hans trick.