When he feels comfortable and familiar, he smiles at you. He has this canine smile, relatively rare, that raises the upper lips and shows teeth and gums, slightly lifting the head. When he doesn't feel comfortable, which is very often, he puts his tail under the legs and skins, not knowing what to do to manage what is stressing him.
Our Morfeas was born on the street, with his mom trying to keep him and his siblings warm and safe there, on the street, under a car. He grew up in the shelter, and that's what he knows, almost nothing else. It is not the dog that will come to meet you by wagging the tail, it is not the dog that you will take home and you will feel from the first moment that you have done him good. He will probably be sitting in a corner in fear, and will stay there for days.
It will open up slowly, with patience, and consistently. After a week, two, three, he will timidly wag his tail. After a month, two, three, he will show you his smile. At some point you will be the most important, the most precious, the most beloved person he has in his life. And then you will feel that you have done him good, that you have changed his life, that you have made the best decision someone has ever made for him.