"... the known experience of the chemist Friederich August von Kekulé. Lots of times it's been observed that the scientific and technological discover discovery often includes a metaforical thinking. In 1865, Kekulé had been trying, with little success, to discover the chemical structure of the benzene. The molecule consists in a ring of atoms, but then they didn't know the structures of the ring. Absort in the problem, Kekulé had a dream in which the molecules appeared like files of atoms. They gathered and swerved in such a way that they made Kekulé think of serpents. Suddenly, one of the serpents turned until biting its tail, and this suggested Kekulé the structure of the benzene ring."