Jacobson’s organ, also called the vomeronasal organ, is a chemoreception organ of that is part of the olfactory system of amphibians, reptiles, and mammals, but does not occur in all tetrapod groups. It is a patch of sensory cells within the main nasal chamber that detects heavy moisture-borne odour particles. Airborne odours, in contrast, are detected by the olfactory sensory cells located in the main nasal chambers. Some groups of mammals also initiate a behaviour known as the flehmen response, in which the animal facilitates the exposure of the vomeronasal organ to a scent or pheromone by opening the mouth and curling the upper lip during inhalation.

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