In this episode, the discussion revolves around competing theories of olfaction, which explore how the olfactory system detects different odor molecules. The docking theory suggests that odorant recognition relies on the shape of the molecule fitting into a specific receptor, much like a key fits into a lock. On the other hand, the vibrational theory, introduced by Luca Turin, proposes that recognition is based on the molecule's unique vibrational frequencies. Turin's theory suggests that olfactory receptors act as inelastic electron tunneling spectrometers, detecting these vibrations and signaling the presence of a specific odor in the brain. The episode also examines various experimental evidence, including the use of deuterium-substituted molecules, to evaluate the validity of these competing theories.