Cats hold their mouth open after smelling something because of their Jacobson’s organ, a special sensory organ called the vomeronasal organ or Jacobson’s organ that allows a cat to have 14 times the sense of smell of a human.
The reason they look dazed for a second or two is because they can learn a lot of information about their surroundings through their sense of smell. They mark territory using the scent glands on their cheeks and paws.
The flehmen response is heavily tied to identifying pheromones, which is extremely important for cats. As such, it plays a huge role in interspecies communication. The vomeronasal organ is olfactory-chemosensory organ which can help animals gather chemical messages from their peers.
In cats, the vomeronasal organ is located inside the roof of their mouths. It has ducts leading to the mouth and the nose called the nasopalatine canals. On the roof of the cat’s mouth, just behind its incisors, you can see two openings.