Flamen reaction is a special behavior of animals with upturned upper lip, which can be seen in ungulates, cats and other mammals.
Introduction:
Many mammals, such as horses, lions, pandas and so on, have the behavior of turning up their upper lips. In daily life, when a domestic cat smells a strong or strange smell, it will also open its mouth half-way, tilt its upper lip, show its teeth and squint its eyes, as if it had been smoked by a strong smell. This reaction is called Flamenco reaction.
Animals can smell not only from their noses, but also from their mouths. For example, there are two tiny holes at the root of the front teeth of the cat's upper jaw (the upper arch in the mouth), which are connected with Jacobson's organs. The odor molecules absorbed here can reach the brain through a different path than the odor inhaled by the nose.
In order to make the nose plow absorb odor molecules, it is necessary to half-open the mouth and raise the upper lip. Turning up the upper lip is beneficial to transfer the smell to the nose plough. With the nose plough, animals can better feel the smell and pheromones.
Animals with olfactory response to cleft lip include horses, cows, elephants, tigers, tapirs, lions, giraffes, goats, alpacas, koalas, hedgehogs, rhinoceroses and giant pandas. The horse's cleft lip sniffs a lot, which is very noticeable. Grinning, like laughing, is a kind of sexual behavior, which is thought to be done in order to be able to perceive the hormones contained in the urine of the opposite sex.