Cat have a far superior sense of smell to humans. Scent, both human and feline is a long time interest of mine. I taught aromatherapy for many years including the anatomy and physiology of the olfactory system. It gave me respect for how remarkable a cat’s sense of smell truly is. Not only do they have more olfactory cells than us but they can turbo-charge their sniffing with help from a tiny organ above the roof of their mouth called Jacobson’s organ aka the vomeronasal organ (VNO).
When a cat (that includes the big cats like lions and tigers) wants to identify scents via pheromones (chemical messengers found in urine and scent glands that detect prey, food, potential mates or mark territories), they open their mouth to scent/taste the air in a Flehman’s response (from German flehmen, meaning to curl the upper lip). They drink in the scent slowly as if intoxicated, and in a sense they are. The scent molecules waft over the VNO and transmitted to hypothalamus, the part of the brain associated with sexual and social interaction.
That funny face is nothing to sniff at. The open mouth allows the scent to pass over the VNO and “fine tune” to ID incoming scents (as demonstrated by Domino in this series of images of scent communication. In this case, there was a vole nearby. Merlin flehmans when he smells Hubby’s underwear and Odin flehmans near certain tree stumps or when he catches a whiff of catnip. I’m joking about Domino’s subjective “good” reaction. Cats don’t have the same emotional response as humans when it comes to scent nor do they judge scents as good or bad unlike humans who have scent associations mingled with memories and emotions. Cats might turn their nose up in disgust at a dirty cat litter box, a toxic substance, or tainted food but it’s a survival mechanism and anything else is anthropomorphizing.