The veterinary visit must always to include a detailed and cared observation of your friend’s mouth. Please be used to make these procedures even by yourself but regularly.
You need to verify that there are no wounds or neoplasm on the lips no matter if benign or aggressive, no presence of excessive saliva, unless it is normal in some races or for abnormal structure of mandible/jaws. You proceed by raising the lips and verifying that the mucosa has a uniform pink color, without wounds and neoplasm, teeth have to be steady with not bleeding gums with a uniform white color; in ancient subjects you often find real plaques of tartar which have to be removed by the veterinary.
Then if it is possible, you will open the mouth completely to observe it inside, tongue included, which has to be mobile and without wounds; if you note ulcers they could even be the result of viral pathologies or of toxic substances. And at the end you have to watch the bottom of the mouth, you often note in cats red and very hurtful wounds which cause difficulties during swallowing.