Updated: Feb 18, 2020
Moose and other animals )ungulates and felids) exhibit a behavior usually during mating season while investigating odors. called the "Fehmen Response." This behavior may be performed over the sight or substance of a particular animal or may be performed with the neck stretched and the head held high.. It is believed they are "odor messages." The animal then curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed, and holds the position from a few seconds to over a minute.
This behavior facilitates the transfer of pheromones and other scents into the vomeronasal organ (VMO or Jacob's organ) located above the roof of the mouth, via a duct which exits just behind the front teeth of the animal.
In moose, this behavior allows the bulls (males) to smell whether a cow (female) is ready to mate and is sexually active.