A cat's slightly open mouth may be due to the hot weather, requiring it to breathe and cool down; secondly, the cat may have smelled an unfamiliar scent and is trying to identify what the surrounding scent is.



However, if a cat's mouth remains slightly open and cannot be closed, the owner should consider whether the cat has rhinitis, pneumonia, or oral ulcers. If the cat also exhibits symptoms such as lethargy or poor appetite, it is recommended that the owner take it to a veterinary hospital to check for the specific cause and receive treatment.