Research overview: the flehmen response in cats

The flehmen response is a distinctive open-mouthed, lip-curled grimace cats make to draw scent molecules into the vomeronasal organ. This overview surveys the behavior and its function, in which a cat encountering an interesting odor, often a scent mark or another cat's chemical signal, pauses with its mouth slightly open and an intent expression. The posture helps transfer non-volatile chemicals to the vomeronasal ducts for analysis. The survey relates flehmen to the detection of pheromones and to social and reproductive communication. It discusses how the behavior is sometimes mistaken for a grimace of disgust when it actually reflects focused chemical investigation. Understanding flehmen links the anatomy of the vomeronasal organ to an observable behavior, showing that cats actively sample certain scents in a specialized way. It is a vivid example of how feline chemical perception extends beyond ordinary sniffing into a dedicated sensory ritual.