Our beagle discovered how to scratch her own back a variety of ways. Her most favorite way would be to go under our daybed and rub her back against the springs. It was just low enough to reach her perfectly. When we couldn't find her anywhere in the house we knew where to look - she would sometimes be under there for hours scooting back and forth with this big cheese grin on her face.
My coonhound would scare herself if she passed gas. She would look back in terror like someone did something to her, then take off running with her tail between her legs like she was frightened. Also, when she would get frightened, a strip of hair down her back would stand straight up like a mohawk - it looked bizarre.
