Hmmm...where to start...
I could list several, but the one thing that strikes me, and others, as odd is that in training class Linus rolls onto the side of his head, imagine a halfway finished somersault with your chin touching your chest, sticks his butt in the air, kicks a back foot, makes weird growling/panting/grunting noises, and wags his tail. Eventually he makes it all the way over and lays there playing with his front paws. When we were in puppy school and waiting for others to do their exercise or if the instructor was helping, I'd play with him on the floor and he'd do this. I guess it stuck!