This is an adorable photo. Forget, if you can, the individual cuteness of each pup. The composition of the whole is striking.
Look at the fellow second from the right. (Your right, as viewer.) He is probably the smallest and cutest of all of them. His individual toes are well defined, whereas for each of the others we have to take a "paw" as the smallest print-establishing unit. So call the little fellow "Toesy." Further, his toes are held back from the line of each of the other's paws, as if he is the most timid member of the crowd.
Now imagine that Toesy isn't in the photo at all. Photoshop him out, and then shorten the tub so he leaves no empty space. You would then have a remarkably symmetrical arrangement of five Sheltie pups.
The middle pup of those five would be the only one howling. The two that flanked him would be (are) the only two with a lot of black fur. And the two that flanked them (again, without Toesy) would be the only two with their tongues hanging out in classic puppy-panting pose.
When I look at this photo, I see that symmetrical arrangement, with Toesy getting in the way as a sort of symmetry-foiler. He is like a dimple on the right cheek of a face, unaccompanied by any dimple on the left cheek. It just makes ther whole face even more wonderful than would perfect symmetry.