A mental patient insisted to a psychiatrist that he had swallowed a horse.

The psychiatrist tried to change the patient's belief by his short speech but failed.

The psychiatrist then anaesthetized the patient and brought in a horse (brown in color) in the theatre to change the patient's wrong belief.

When the patient sailed out of anesthesia, he was shown the horse which had been removed from his body, and was told that now he should feel O.K.

The patient responded angrily, "Doctor it was a white horse, and not a brown horse".

Thus, the psychiatrist's trick failed.