organ contracts or pumps in order to draw in the scents. Flehmen response Some mammals, particularly felids (cats) and ungulates (which includes horses, cattle, and pigs among other species), use a distinctive facial movement called the flehmen response to direct inhaled compounds to the VNO. The animal lifts its head after finding the odorant, wrinkles its nose while lifting its lips, and ceases to breathe momentarily. Flehmen behavior is associated with “anatomical specialization”, and animals that present flehmen behavior have incisive papilla and ducts, which connect the oral cavity to the VNO, that are found behind their teeth. However, horses are the exception: they exhibit flehmen response but do not have an incisive duct communication between the nasal and the oral cavity because they do not breathe through their mouths; instead, the VNOs connect to the nasal passages by the nasopalatine duct. Cats use their vomeronasal organ when scent rubbing; they are able to discriminate between similar smelling substances using this organ, and then perform the rubbing behaviour. Evidence for existence in humans Many studies have tried to determine whether there is a VNO in adult human beings. Trotier et al. estimated that around 92% of their subjects that had no septal surgery had at least one intact VNO. Kjaer and Fisher Hansen, on the other hand, stated that the VNO structure disappears during fetal development as it does for some primates. However, Smith and Bhatnagar (2000) asserted that Kjaer and Fisher Hansen simply missed the structure in older fetuses. Won (2000) found evidence of a VNO in 13 of his 22 cadavers (59.1%) and 22 of his 78 living patients (28.2%). In a study using retrospective analysis of nearly one thousand outpatient nasal endoscopies, Stoyanov et al. (2016) found the organ to be present in 26.83% of the Bulgarian population. Given these findings, some scientists have argued that there is a VNO in adult human beings. However, most investigators have sought to identify the opening of the VNO in humans, rather than identify the tubular epithelial structure itself. Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes misidentified or even missed the vomeronasal organ. Among studies that use microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals. Furthermore, there is no evidence to date that suggests there are nerve and