In the case of this mouth the lips are not in a position to completely close over the teeth.
If they do close over the teeth, then the face may express tension.
In this case, be assured that what you see is what you get from these people. There is no hiding of emotions. These people are honest and trustworthy. They do not distort facts at all. They only show what is in their hearts. It is hard for these people to lie.
The truth is always seen in their facial expressions, they are easy to read. Their sincerity is admirable. These people do not show off or boast. That is not their nature. They actually do not like people who boast in any manner.
People who have this mouth are good listeners.
When they get access to some of your secrets, they can keep them well. These people cannot be trusted. They make great friends who are long lasting. When you reveal everything to these people, you do not have to get worried. They do not like talking without purpose.