That discovery was the first to offer proof that some pheromones may serve as behavior modulators, rather than triggering specific, predictable actions. Like other scientists, McClintock has been looking in the nose. This accessory olfactory system is different from the sense of smell, the receptors for which are in the olfactory epithelium in the nose. Apes stick out their tongues, collect chemical signals and deposit them in two pits in the roof of their mouth. The holes, called the nasal palatine ducts, take the pheromones to the nose and travel to the brain.
Dogs also have such an open duct connecting the oral and nasal cavities.
So do elephants, it was recently discovered. McClintock believes people do as well. The presence of a human VNO is controversial in science, and I'd never seen one. But it is symmetrical and easily detectable, if you know what you're looking for. It's consistently found near the juncture of the nasal septum and the floor of the nasal cavity.