I wonder if you have found a problem, that is, why cats open their mouths when they smell stinky feet. I have discovered it many times. Because I am very curious about it, I will analyze why cats open their mouths when they smell stinky feet.
After cats smell smelling smelly feet, they will indeed open their mouths and show a terrified expression. But this is not what they are spitting out. Instead, they are just turning up the upper lip to allow the odor to enter the nasal cavity so that the odor can be sensed better. This behavior is called "cleaved lip sniffing reaction".
Many mammals actually have this behavior of turning their upper lips up, such as horses, lions, pandas, etc. In daily life, when ordinary domestic cats smell a strong smell, they will half open their mouths, lift their upper lip, reveal their teeth, and squint their eyes. It looks like they are smelled by the smell. In fact, this is a cracked lip sniff. There are two small holes at the root of the anterior teeth of the upper palate (the upper arched part of the mouth) connected to the covolar device. The scent molecules absorbed from here can be sniffed into different paths from the nose to reach the brain. In order to allow the odor molecules to be absorbed by the covorarin, the mouth must be half opened and the upper lip must be lifted.