flehmen

Also called fleh·men re·sponse [fley, -m, uh, n ri-spons],. a behavioral response of many mammals, especially deer and other artiodactyls, felines, and horses, consisting of raising the head and curling the upper lip to aid the sense of smell by increasing the flow of air through the nostrils and exposing the auxiliary olfactory organs: often a response to the detection of pheromones. lip curl ( def 1b ).

(of deer, horses, and many other mammals) to raise the head and curl the upper lip to aid the sense of smell by increasing the flow of air through the nostrils and exposing the auxiliary olfactory organs.