Flehmen response in a horse. The flehmen response (/ˈfleɪmən/; German: [ˈfleːmən]), also called the flehmen position, flehmen reaction, 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.