裂唇嗅反应（flehmen response），意指翻起上唇。裂唇嗅为上唇翻起之特殊行为，可见于有蹄类动物、猫科动物及其他哺乳类动物(如：熊猫)。此行为有利于信息素与其他气味传递至犁鼻器。动物行裂唇嗅时将唇部后翻使其脸部状似「扭曲」。用于探察其他同类动物或猎物留下之气味，并帮助犁鼻器曝露及接收气味。也用于探察其他种类动物及猎物留下之气味，如：尿液。动物借此行为判断许多状态因子，如动情期的出现、生理机能状态或其他动物离去时间的长短。目前已认可的是当雄马嗅知发情母马的气味时会出现此行为。

该词源自于德文动词 flehmen ，裸露上排牙齿之意；或是上盎格鲁德语方言 flemmen ，形容面目可憎的样子。

The flehmen response (/ˈfleɪmən/; German:[ˈfleːmən]), also called the flehmen position, flehmen reaction, flehming, or flehmening, is a behaviour whereby 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. It may be performed over a site or substance of particular interest to the animal (e.g. urine or faeces) or may be performed with the neck stretched and the head held high in the air. Flehmen is performed by a wide range of mammals including ungulates and felids. The behaviour facilitates the transfer of pheromones and other scents into the vomeronasal organ located above the roof of the mouth via a duct which exits just behind the front teeth of the animal.