wikipedia

The flehmen response (/ˈfleɪmən/; from German flehmen 'to bare the upper teeth', and Upper Saxon German flemmen 'to look spiteful'), also called the flehmen position, flehmen reaction, flehmen grimace, flehming, or flehmening, is a behavior in which an animal curls back its upper lip exposing its front teeth, inhales with the nostrils usually closed, and then often holds this position for several seconds.[1] It may be performed over a site or substance of particular interest to the animal, or may be performed with the neck stretched and the head held high in the air.