Sometimes Finn has the ability to make himself disappear -he usually does this when he's in some sort of trouble.
In this picture, he is completely invisible.
Any impression that you may have that you can in any way see a corgi here is purely the result of a photographic anomoly.
The fun thing about this is that if you walk up to him and poke one of his toes with your finger, that toe and the half of his butt that it is attached to will slowly disappear under the bed, leaving the other toe and the other half of his butt sticking out. Then if you poke the other toe, that toe and the other half of his butt will slowly disappear under the bed.
He thinks he's so slick.